Bulk acoustic wave resonators with patterned mass loading layers

ABSTRACT

Aspects of this disclosure relate to bulk acoustic wave resonators with patterned mass loading layers. Two different bulk acoustic wave resonators of an acoustic wave filter and/or an acoustic wave die have respective patterned mass loading layers with different densities. The patterned mass loading layers contribute to the two different bulk acoustic wave resonators having different respective resonant frequencies. Related bulk acoustic wave devices, filters, acoustic wave dies, radio frequency modules, wireless communication devices, and methods are disclosed.

CROSS REFERENCE TO PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 C.F.R. § 1.57.This application claims the benefit of priority of U.S. ProvisionalApplication No. 62/085,413, filed Sep. 30, 2020 and entitled “BULKACOUSTIC WAVE RESONATORS WITH PATTERNED MASS LOADING LAYERS,” U.S.Provisional Application No. 62/085,399, filed Sep. 30, 2020 and entitled“BULK ACOUSTIC WAVE RESONATOR WITH MASS LOADING LAYER,” and U.S.Provisional Application No. 62/085,398, filed Sep. 30, 2020 and entitled“METHODS OF MANUFACTURING BULK ACOUSTIC WAVE RESONATORS WITH PATTERNEDMASS LOADING LAYERS,” the disclosures of each of which are herebyincorporated by reference in their entireties.

BACKGROUND Technical Field

Embodiments of this disclosure relate to acoustic wave devices and, morespecifically, to bulk acoustic wave devices.

Description of Related Technology

Acoustic wave filters can be implemented in radio frequency electronicsystems. For instance, filters in a radio frequency front end of amobile phone can include one or more acoustic wave filters. A pluralityof acoustic wave filters can be arranged as a multiplexer. For instance,two acoustic wave filters can be arranged as a duplexer.

An acoustic wave filter can include a plurality of resonators arrangedto filter a radio frequency signal. Example acoustic wave filtersinclude surface acoustic wave (SAW) filters and bulk acoustic wave (BAW)filters. BAW filters include BAW resonators. Example BAW resonatorsinclude film bulk acoustic wave resonators (FBARs) and solidly mountedresonators (SMRs). In BAW resonators, acoustic waves propagate in a bulkof a piezoelectric layer.

Manufacturing BAW resonators having different resonant frequencies caninvolve several processing steps. As more BAW resonators with differentresonant frequencies are being manufactured on a common die, the numberof processing steps to manufacture such BAW resonators can alsoincrease.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

The innovations described in the claims each have several aspects, nosingle one of which is solely responsible for its desirable attributes.Without limiting the scope of the claims, some prominent features ofthis disclosure will now be briefly described.

One aspect of this disclosure is an acoustic wave filter that includes afirst bulk acoustic wave resonator and a second bulk acoustic waveresonator. The first bulk acoustic wave resonator includes a firstpatterned mass loading layer having a first density. The first patternedmass loading layer impacts a resonant frequency of the first bulkacoustic wave resonator. The second bulk acoustic wave resonatorincludes a second patterned mass loading layer having a second density.The second patterned mass loading layer impacts a resonant frequency ofthe second bulk acoustic wave resonator. The second density is differentthan the first density. The bulk acoustic wave filter is arranged tofilter a radio frequency signal.

The first and second patterned mass loading layers can be formed duringa common processing step. The first patterned mass loading layer canextend from a first piezoelectric layer of the first bulk acoustic waveresonator a same distance as the second patterned mass loading layerextends from a second piezoelectric layer of the second bulk acousticwave resonator.

The first patterned mass loading layer can have a periodic pattern. Thefirst patterned mass loading layer can include a plurality of stripsspaced apart from each other. The first patterned mass loading layer caninclude a first group of strips and a second group of strips thatintersect with the first group of strips. The first patterned massloading layer can have a concentric pattern.

The first patterned mass loading layer can include a different materialthan any other layer of the first bulk acoustic wave resonator inphysical contact with the first patterned mass loading layer.Alternatively, the first patterned mass loading layer can include a samematerial as a layer of the first bulk acoustic wave resonator inphysical contact with the first patterned mass loading layer. The firstpatterned mass loading layer can include a metal. The first patternedmass loading layer can include a dielectric material.

The first patterned mass loading layer can be positioned below apiezoelectric layer of the first bulk acoustic wave resonator.Alternatively, the first patterned mass loading layer can be positionedabove a piezoelectric layer of the first bulk acoustic wave resonator.The first patterned mass loading layer can be positioned over anelectrode positioned over a piezoelectric layer of the first bulkacoustic wave resonator.

The acoustic wave filter can include a third bulk acoustic waveresonator that includes a third patterned mass loading layer having athird density, in which the third density is different than both thefirst density and the second density.

The first bulk acoustic wave resonator can be a film bulk acoustic waveresonator.

The second density can be higher than the first density, and theresonant frequency of the second bulk acoustic wave resonator can belower than the resonant frequency of the first bulk acoustic waveresonator. A resonant frequency of the first bulk acoustic waveresonator can be in a range from 0.1% to 10% greater than a resonantfrequency of the second bulk acoustic wave resonator. A resonantfrequency of the first bulk acoustic wave resonator can be in a rangefrom 1% to 10% greater than a resonant frequency of the second bulkacoustic wave resonator.

The first patterned mass loading layer can have a duty factor in a rangefrom 0.05 to 0.95 in a main acoustically active region of the first bulkacoustic wave resonator. The first patterned mass loading layer can havea duty factor in a range from 0.2 to 0.8 in a main acoustically activeregion of the first bulk acoustic wave resonator. The second patternedmass loading layer can have a duty factor in a range from 0.05 to 0.95in a main acoustically active region of the second bulk acoustic waveresonator. The second patterned mass loading layer can have a dutyfactor in a range from 0.2 to 0.8 in a main acoustically active regionof the second bulk acoustic wave resonator.

Another aspect of this disclosure is an acoustic wave filter thatincludes a first bulk acoustic wave resonator and a second bulk acousticwave resonator. The first bulk acoustic wave resonator includes a firstpatterned mass loading layer and a periodic pattern. The second bulkacoustic wave resonator includes a second patterned mass loading layer.The second mass loading provides greater mass loading than the firstpatterned mass loading layer such that the second patterned mass loadinglayer causes the second bulk acoustic wave resonator to have a lowerresonant frequency than the first bulk acoustic wave resonator. The bulkacoustic wave filter is arranged to filter a radio frequency signal.

Another aspect of this disclosure is an acoustic wave die that includesa first bulk acoustic wave resonator on the bulk acoustic wave die and asecond bulk acoustic wave resonator on the bulk acoustic wave die. Thefirst bulk acoustic wave resonator includes a first patterned massloading layer having a first density. The first patterned mass loadinglayer impacts a resonant frequency of the first bulk acoustic waveresonator. The second bulk acoustic wave resonator includes a secondpatterned mass loading layer having a second density. The second densityis higher than the first density. The second patterned mass loadinglayer impacts a resonant frequency of the second bulk acoustic waveresonator.

The first bulk acoustic wave resonator and the second bulk acoustic waveresonator can be included in a same filter. Alternatively, the firstbulk acoustic wave resonator and the second bulk acoustic wave resonatorcan be included in different filters. Such different can be filters areincluded in a multiplexer.

The first and second patterned mass loading layers can be formed duringa common processing step. The first patterned mass loading layer canextend from a first piezoelectric layer of the first bulk acoustic waveresonator a substantially same distance as the second patterned massloading layer extends from a second piezoelectric layer of the secondbulk acoustic wave resonator.

The first patterned mass loading layer can have a periodic pattern. Thefirst patterned mass loading layer can include a plurality of stripsspaced apart from each other.

The first patterned mass loading layer can include a different materialthan any other layer of the first bulk acoustic wave resonator inphysical contact with the first patterned mass loading layer.Alternatively, the first patterned mass loading layer can include a samematerial as a layer of the first bulk acoustic wave resonator inphysical contact with the first patterned mass loading layer. The firstpatterned mass loading layer can include a metal. The first patternedmass loading layer can include a dielectric material.

The acoustic wave die can include a third bulk acoustic wave resonatorthat includes a third patterned mass loading layer having a thirddensity, in which the third density is different than both the firstdensity and the second density.

A resonant frequency of the first bulk acoustic wave resonator can be ina range from 0.1% to 10% greater than a resonant frequency of the secondbulk acoustic wave resonator. A resonant frequency of the first bulkacoustic wave resonator can be in a range from 1% to 10% greater than aresonant frequency of the second bulk acoustic wave resonator.

The first patterned mass loading layer can have a duty factor in a rangefrom 0.05 to 0.95 in a central area of an active region of the firstbulk acoustic wave resonator. The first patterned mass loading layer canhave a duty factor in a range from 0.2 to 0.8 in a central area of anactive region of the first bulk acoustic wave resonator.

Another aspect of this disclosure is a radio frequency module thatincludes an acoustic filter with a bulk acoustic wave device having apatterned mass loading layer and a radio frequency circuit elementcoupled to the acoustic wave filter. The acoustic wave filter and theradio frequency circuit element are enclosed within a common modulepackage.

The radio frequency circuit element can be a radio frequency amplifierarranged to amplify a radio frequency signal. The radio frequencycircuit element can be a switch configured to selectively couple theacoustic wave filter to a port of the radio frequency module.

Another aspect of this disclosure is a wireless communication devicethat includes an acoustic wave filter with a bulk acoustic wave devicehaving a patterned mass loading layer, an antenna operatively coupled tothe acoustic wave filter, a radio frequency amplifier operativelycoupled to the acoustic wave filter and configured to amplify a radiofrequency signal, and a transceiver in communication with the radiofrequency amplifier.

The wireless communication device can include a baseband processor incommunication with the transceiver. The acoustic wave filter can beincluded in a radio frequency front end. The wireless communicationdevice can be a user equipment.

Another aspect of this disclosure is a bulk acoustic wave resonator thatincludes a first electrode over an acoustic reflector, a piezoelectriclayer over the first electrode, a second electrode over thepiezoelectric layer, and a patterned mass loading layer having a dutyfactor in a range from 0.2 to 0.8 in a main acoustically active regionof the bulk acoustic wave resonator. The patterned mass loading layer isarranged to affect a resonant frequency of the bulk acoustic waveresonator.

The patterned mass loading layer can have a periodic pattern. Thepatterned mass loading layer can include a plurality of strips spacedapart from each other. The patterned mass loading layer can have a dutyfactor in a range from 0.3 to 0.7 in the main acoustically activeregion.

The patterned mass loading layer can include a different material thanany other layer of the bulk acoustic wave resonator in physical contactwith the patterned mass loading layer. The patterned mass loading layercan include a same material as a layer of the bulk acoustic waveresonator in physical contact with the patterned mass loading layer. Thepatterned mass loading layer can include a metal. The patterned massloading layer can include a dielectric material.

The patterned mass loading layer can be positioned below thepiezoelectric layer. The patterned mass loading layer can be positionedabove the piezoelectric layer. The patterned mass loading layer can bepositioned over the second electrode.

The acoustic reflector can be an air cavity. Alternatively, the acousticreflector can be is a solid acoustic mirror.

Another aspect of this disclosure is an acoustic wave filter thatincludes a bulk acoustic wave resonator and a plurality of additionalacoustic wave resonators. The bulk acoustic wave resonator includes afirst electrode over an acoustic reflector, a piezoelectric layer overthe first electrode, a second electrode over the piezoelectric layer,and a patterned mass loading layer having a duty factor in a range from0.2 to 0.8 in a main acoustically active region of the bulk acousticwave resonator. The patterned mass loading layer is arranged to affect aresonant frequency of the bulk acoustic wave resonator. The acousticwave filter is configured to filter a radio frequency signal.

The patterned mass loading layer can have a periodic pattern. The bulkacoustic wave resonator can be a series resonator. The bulk acousticwave resonator can be a shunt resonator.

The filter can be included in a wireless communication device that alsoincludes an antenna operatively coupled to the acoustic wave filter, aradio frequency amplifier operatively coupled to the acoustic wavefilter and configured to amplify a radio frequency signal, and atransceiver in communication with the radio frequency amplifier. Thewireless communication device can include a baseband processor incommunication with the transceiver. The acoustic wave filter can beincluded in a radio frequency front end. The wireless communicationdevice can be a user equipment.

Another aspect of this disclosure is a method of manufacturing bulkacoustic wave resonators. The method includes providing a bulk acousticwave resonator structure including a support substrate; and during acommon processing step, forming (i) a first patterned mass loading layeron the bulk acoustic wave resonator structure in a first area for afirst bulk acoustic wave resonator and (ii) a second patterned massloading layer on the bulk acoustic wave resonator structure in a secondarea for a second bulk acoustic wave resonator. The second patternedmass loading layer has a different density than the first patterned massloading layer.

The bulk acoustic wave resonator structure can include a passivationlayer and an electrode layer. The bulk acoustic wave resonator structurecan also include a piezoelectric layer. The bulk acoustic wave resonatorstructure can also include a second electrode layer, where thepiezoelectric layer is positioned between the first electrode layer andthe second electrode layer. The bulk acoustic wave resonator structurecan also include a second passivation layer over the second electrodelayer.

The first patterned mass loading layer can include a different materialthan any layer of the first bulk acoustic wave resonator that is inphysical contact with the first patterned mass loading layer.Alternatively, the first patterned mass loading layer and a layer of thefirst bulk acoustic wave resonator structure that is in physical contactwith the first patterned mass loading layer can both be of a samematerial. The first patterned mass loading layer can include adielectric material. The first patterned mass loading layer can includea metal.

The method can also include forming, during the common processing step,a third patterned mass loading layer over the bulk acoustic waveresonator structure in a third area for a third bulk acoustic waveresonator. The third patterned mass loading layer has a differentdensity than both the first and second patterned mass loading layers.

The common processing step can include depositing material of the firstand second patterned layers. The common processing step can includeremoving material to form the first and second patterned layers.

The method can further include forming, during the common processingstep, a third patterned mass loading layer over the bulk acoustic waveresonator structure in a third area for a third bulk acoustic waveresonator; and removing material to increase a depth between features ofthe third patterned mass loading layer. The depth between the featuresof the third patterned mass loading layer can be greater than a depthbetween features of the first patterned mass loading layer.

The first patterned mass loading layer can have a periodic pattern. Thefirst patterned mass loading layer can include a plurality of stripsspaced apart from each other. The first patterned mass loading layer caninclude a first group of strips and a second group of strips thatintersect with the first group of strips. The first patterned massloading layer can have a concentric pattern.

The first bulk acoustic wave resonator can be a film bulk acoustic waveresonator. Alternatively, the first bulk acoustic wave resonator can bea solidly mounted resonator.

The method can include interconnecting a plurality of bulk acoustic waveresonators such that the first and second bulk acoustic wave resonatorsare included in a common filter. Alternatively, the can includeinterconnecting a plurality of bulk acoustic wave resonators such thatthe first bulk acoustic wave resonator is included in a first filter andthe second bulk acoustic wave resonator is included in a second filter.A multiplexer can include the first filter and the second filter. Themultiplexer can be a duplexer.

After manufacture, the first patterned mass loading layer can impact aresonant frequency of the first bulk acoustic wave resonator and thesecond patterned mass loading layer can impact a resonant frequency ofthe second bulk acoustic wave resonator. The resonant frequency of thefirst bulk acoustic wave resonator can be in a range from 0.1% to 10%greater than the resonant frequency of the second bulk acoustic waveresonator. The resonant frequency of the first bulk acoustic waveresonator can be in a range from 1% to 10% greater than the resonantfrequency of the second bulk acoustic wave resonator.

The first patterned mass loading layer can have a duty factor in a rangefrom 0.05 to 0.95 in a main acoustically active region of the first bulkacoustic wave resonator. The second patterned mass loading layer canhave a duty factor in a range from 0.05 to 0.95 in a main acousticallyactive region of the second bulk acoustic wave resonator.

The first patterned mass loading layer can have a duty factor in a rangefrom 0.2 to 0.8 in a main acoustically active region of the first bulkacoustic wave resonator. The second patterned mass loading layer canhave a duty factor in a range from 0.2 to 0.8 in a main acousticallyactive region of the second bulk acoustic wave resonator.

Another aspect of this disclosure is a method of manufacturing bulkacoustic wave resonators. The method includes providing a bulk acousticwave resonator structure including a support substrate; and during acommon processing step, depositing material to form (i) a firstpatterned mass loading layer over the bulk acoustic wave resonatorstructure in a first area for a first bulk acoustic wave resonator and(ii) a second patterned mass loading layer over the bulk acoustic waveresonator structure in a second area for a second bulk acoustic waveresonator, the second patterned mass loading layer having a differentdensity than the first patterned mass loading layer.

Another aspect of this disclosure is a method of manufacturing bulkacoustic wave resonators. The method includes providing a bulk acousticwave resonator structure including a support substrate; and during acommon processing step, etching material to form (i) a first patternedmass loading layer on the bulk acoustic wave resonator structure in afirst area for a first bulk acoustic wave resonator and (ii) a secondpatterned mass loading layer on the bulk acoustic wave resonatorstructure in a second area for a second bulk acoustic wave resonator,the second patterned mass loading layer having a different density thanthe first patterned mass loading layer.

Another aspect of this disclosure is a bulk acoustic wave resonator thatincludes a first electrode over an acoustic reflector, a piezoelectriclayer over the first electrode, a second electrode over thepiezoelectric layer, and a patterned mass loading layer at leastcontributing to a difference in mass loading between a main acousticallyactive region and a recessed frame region. The patterned mass loadinglayer is arranged to affect a resonant frequency of the bulk acousticwave resonator.

The patterned mass loading can be included in both the main acousticallyactive region and the recessed frame region, and the patterned massloading layer can have a higher density in the main acoustically activeregion than in the recessed frame region.

The patterned mass loading layer can be included in the mainacoustically active region, and the recessed frame region can be freefrom the patterned mass loading layer.

The patterned mass loading layer can have a periodic pattern in thefirst area. The patterned mass loading layer can include a plurality ofstrips spaced apart from each other.

The patterned mass loading layer can include a different material thanany layer of the bulk acoustic wave resonator that is in physicalcontact with the patterned mass loading layer. The patterned massloading layer and a layer of the bulk acoustic wave resonator structurethat is in physical contact with the patterned mass loading layer canboth be of a same material.

The patterned mass loading layer can have a duty factor that is notgreater than 0.3 in the second area. The patterned mass loading layercan have a duty factor in a range from 0.05 to 0.3 in the second area.The patterned mass loading layer can have a duty factor in the firstarea that is greater than the duty factor in the second area. Thepatterned mass loading layer can have a duty factor in a range from 0.3to 0.8 in the first area.

Another aspect of this disclosure is an acoustic wave filter thatincludes a bulk acoustic wave resonator and a plurality of additionalacoustic wave resonators. The bulk acoustic wave resonator includes afirst electrode over an acoustic reflector, a piezoelectric layer overthe first electrode, a second electrode over the piezoelectric layer,and a patterned mass loading layer at least contributing to a differencein mass loading between a main acoustically active region and a recessedframe region. The patterned mass loading layer is arranged to affect aresonant frequency of the bulk acoustic wave resonator. The acousticwave filter is configured to filter a radio frequency signal.

Another aspect of this disclosure is a method of manufacturing a bulkacoustic wave resonator. The method includes providing a bulk acousticwave resonator structure including a support substrate; and during acommon processing step, forming a patterned mass loading layer on thebulk acoustic wave resonator structure such that the patterned massloading layer has a first density in a first area of the bulk acousticwave resonator structure and a second density in a second area of thebulk acoustic wave resonator structure. The first area corresponds to amain acoustically active region of the bulk acoustic wave resonator. Thesecond area corresponds to a recessed frame region of the bulk acousticwave resonator. The first density is higher than the second density.

The method can further include forming a passivation layer over an upperelectrode of the bulk acoustic wave resonator without etching materialof the passivation layer over the recessed frame region, in which theupper electrode is over a piezoelectric layer of the bulk acoustic waveresonator.

The patterned mass loading layer can have a duty factor that is notgreater than 0.3 in the second area. The patterned mass loading layercan have a duty factor in a range from 0.05 to 0.3 in the second area.The patterned mass loading layer can have a duty factor in the firstarea that is greater than the duty factor in the second area. Thepatterned mass loading layer can have a duty factor in a range from 0.3to 0.8 in the first area.

The bulk acoustic wave resonator structure can include a passivationlayer over the support substrate, an electrode layer over thepassivation layer, and a piezoelectric layer over the electrode layer,in which the patterned mass loading layer is formed over thepiezoelectric layer. The bulk acoustic wave resonator structure caninclude a passivation layer over the support substrate, a firstelectrode layer over the passivation layer, a piezoelectric layer overthe first electrode layer, and a second electrode over the piezoelectriclayer, in which the patterned mass loading layer is formed over thesecond electrode.

The common processing step can include depositing material of thepatterned mass loading layer. The common processing step can includeremoving material to form the patterned mass loading layer.

The patterned mass loading layer can have a periodic pattern in thefirst area. The patterned mass loading layer can include a plurality ofstrips spaced apart from each other.

The present disclosure relates to U.S. patent application No. ______[Attorney Docket SKYWRKS.1128A2], titled “BULK ACOUSTIC WAVE RESONATORWITH MASS LOADING LAYER,” filed on even date herewith, the entiredisclosure of which is hereby incorporated by reference herein. Thepresent disclosure relates to U.S. patent application No. ______[Attorney Docket SKYWRKS.1128A3], titled “METHODS OF MANUFACTURING BULKACOUSTIC WAVE RESONATORS WITH PATTERNED MASS LOADING LAYERS,” filed oneven date herewith, the entire disclosure of which is herebyincorporated by reference herein. The present disclosure relates to U.S.patent application No. ______ [Attorney Docket SKYWRKS.1128A4], titled“BULK ACOUSTIC WAVE RESONATOR WITH PATTERNED MASS LOADING LAYER ANDRECESSED FRAME,” filed on even date herewith, the entire disclosure ofwhich is hereby incorporated by reference herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of this disclosure will now be described, by way ofnon-limiting example, with reference to the accompanying drawings.

FIG. 1A is a schematic cross-sectional diagram of a bulk acoustic wave(BAW) resonator according to an embodiment.

FIG. 1B is an example plan view of the BAW resonator of FIG. 1A.

FIG. 1C is another example plan view of the BAW resonator of FIG. 1A.

FIG. 2 includes a schematic cross-sectional view of the material stackof the BAW resonator of FIG. 1A.

FIG. 3 includes a schematic cross-sectional view of the material stackof a BAW resonator with a patterned mass loading layer according to anembodiment.

FIG. 4 includes a schematic cross-sectional view of the material stackof a BAW resonator with a patterned mass loading layer according to anembodiment.

FIG. 5 is a schematic cross-sectional view of a material stack of a BAWresonator with a patterned mass loading layer over a lower electrodeaccording to an embodiment.

FIG. 6 is a schematic cross-sectional view of the material stack of aBAW resonator with a patterned mass loading layer below a lowerelectrode according to an embodiment.

FIG. 7 is a schematic cross-sectional view of the material stack of aBAW resonator with a patterned mass loading layer below a lowerpassivation layer according to an embodiment.

FIG. 8 is a schematic cross-sectional view of the material stack of aBAW resonator with a patterned mass loading layer over an upperelectrode according to an embodiment.

FIG. 9 is a schematic cross-sectional view of the material stack of aBAW resonator with a patterned mass loading layer below a lowerpassivation layer according to an embodiment according to anotherembodiment.

FIG. 10 is a schematic cross-sectional view of the material stack of aBAW resonator with a patterned mass loading layer below a lowerelectrode according to an embodiment according to another embodiment.

FIG. 11 is a schematic cross-sectional view of the material stack of aBAW resonator with a patterned mass loading layer embedded in an upperpassivation layer according to an embodiment.

FIG. 12 is a schematic cross-sectional view of the material stack of aBAW resonator with a patterned mass loading layer embedded in a lowerpassivation layer according to an embodiment.

FIG. 13 is a schematic cross-sectional view of the material stack of aBAW resonator with a patterned mass loading layer embedded in an upperelectrode layer according to an embodiment.

FIG. 14 is a schematic cross-sectional view of the material stack of aBAW resonator with a patterned mass loading layer embedded in a lowerpassivation layer according to an embodiment.

FIG. 15A includes a cross-sectional view of a BAW material stackaccording to an embodiment. FIGS. 15B to 15H illustrate example shapesfor gratings of a patterned mass loading layer.

FIGS. 16A, 16B, and 16C illustrate example patterned mass loading layerswith line patterns in plan view.

FIGS. 17A, 17B, 17C, and 17D illustrate example patterned mass loadinglayers with loop patterns in plan view.

FIGS. 18A and 18B illustrate example patterned mass loading layers withcrossed line patterns in plan view. FIGS. 18C, 18D, and 18E illustrateother example patterned mass loading layers.

FIGS. 19A to 19C illustrate example patterned mass loading layers withdifferent features types for line patterns in plan view.

FIG. 20A shows a plan view of a patterned mass loading layer thatincludes a plurality of line features over an underlying layer. FIG. 20Bshows a side view of the line features of the patterned mass loadinglayer and the underlying layer. FIG. 20C is a graph of simulationresults for the patterned mass loading layer of FIGS. 20A and 20B.

FIG. 21 is a schematic diagram of a ladder filter that includes aplurality of BAW resonators.

FIG. 22 is an example schematic cross-sectional diagram showing materialstacks of example BAW resonators of the ladder filter of FIG. 21 withdifferent patterned mass loading layers.

FIGS. 23A and 23B are flow diagrams of example methods of forming BAWresonators with patterned mass loading layers.

FIGS. 24A and 24B illustrate different schematic cross sections ofmaterial stacks of BAW resonators corresponding to steps of theprocesses of FIGS. 23A and/or 23B.

FIG. 25 is a flow diagram for a process of manufacturing BAW resonators.

FIG. 26 is a top plan view schematically illustrating a BAW die thatincludes BAW resonators with different patterned mass loading layersaccording to an embodiment.

FIG. 27 is a top plan view schematically illustrating a BAW die thatincludes BAW resonators with different patterned mass loading layersaccording to an embodiment.

FIG. 28 is a schematic cross-sectional diagram of a solidly mountedresonator (SMR) with a patterned mass loading layer according to anembodiment.

FIG. 29A is a schematic cross-sectional diagram of a main acousticallyactive region and a recessed frame region of part of a BAW resonatorwith a patterned mass loading layer. FIG. 29B is a schematiccross-sectional diagram of a main acoustically active region and arecessed frame region of part of another BAW resonator with a patternedmass loading layer.

FIG. 30 is flow diagram of an example method of forming a BAW resonatorwith a patterned mass loading layer having a higher density in a mainacoustically active region and a lower density in a raised frame regionaccording to an embodiment.

FIG. 31A is a schematic cross-sectional diagram of part of a BAWresonator with a patterned mass loading layer in a main acousticallyactive region and a recessed frame region without a patterned massloading layer. FIG. 31B is a schematic cross-sectional diagram of partof a BAW resonator with a patterned mass loading layer with a higherdensity in a main acoustically active region than in a recessed frameregion. FIG. 31C is a schematic cross-sectional diagram of part of a BAWresonator with a patterned mass loading layer with a higher density in amain acoustically active region than in a recessed frame region.

FIG. 32A is a plan view of a BAW resonator with a patterned mass loadinglayer. FIG. 32B is a plan view of a BAW resonator with a patterned massloading layer and a recessed frame region without the patterned massloading layer.

FIG. 33A is schematic diagram of an acoustic wave filter. FIG. 33B is aschematic diagram of a duplexer that includes an acoustic wave filteraccording to an embodiment. FIG. 33C is a schematic diagram of amultiplexer that includes an acoustic wave filter according to anembodiment. FIG. 33D is a schematic diagram of a multiplexer thatincludes an acoustic wave filter according to an embodiment. FIG. 33E isa schematic diagram of a multiplexer that includes an acoustic wavefilter according to an embodiment.

FIGS. 34, 35, 36, 37, and 38 are schematic block diagrams ofillustrative packaged modules according to certain embodiments.

FIG. 39 is a schematic diagram of one embodiment of a mobile device.

FIG. 40 is a schematic diagram of one example of a communicationnetwork.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following description of certain embodiments presents variousdescriptions of specific embodiments. However, the innovations describedherein can be embodied in a multitude of different ways, for example, asdefined and covered by the claims. In this description, reference ismade to the drawings where like reference numerals can indicateidentical or functionally similar elements. It will be understood thatelements illustrated in the figures are not necessarily drawn to scale.Moreover, it will be understood that certain embodiments can includemore elements than illustrated in a drawing and/or a subset of theelements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

Bulk acoustic wave (BAW) filters with BAW resonators have a plurality ofdifferent resonant frequencies can meet a variety of designspecifications including insertion loss at a pass band edge, rejectionoutside of a passband of the BAW filter, power handling, and matching toa power amplifier and/or a low noise amplifier. Manufacturing BAWresonators with a plurality of different resonant frequencies with alower complexity process is desirable.

Aspects of this disclosure relate to BAW resonators having differentpatterned mass loading layers and methods of manufacturing such BAWresonators. BAW resonators with different patterned mass loading layerscan have different resonant frequencies. Patterned mass loading layerswith different densities can achieve different mass loading that resultsin such different resonant frequencies. A BAW resonator with a lowerdensity patterned mass loading layer can have a higher resonantfrequency than another BAW resonator that is the same except for havinga higher density patterned mass loading layer. In certain instances, thepatterned mass loading layer can include a plurality of mass loadingstrip lines arranged in a periodic pattern. Material of the patternedmass loading layer can be denser than material of another layer inphysical contact with the patterned mass loading layer. Althoughembodiments may be discussed with reference to BAW resonators, anysuitable principles and advantages disclosed herein can be implementedin any suitable BAW device.

Density of a patterned mass loading layer can tune resonant frequency ofa BAW resonator. A patterned mass loading layer can have a duty factorin a range from 0.05 to 0.95 in a central area of an active region ofthe BAW resonator. Increasing density of the patterned mass loadinglayer can decrease the resonant frequency. On the other hand, decreasingdensity of the patterned mass loading layer can increase the resonantfrequency.

Any two BAW resonators of a filter can be tuned differently by havingpatterned mass loading layers with different densities. For example, twoseries BAW resonators of a filter can have patterned mass loading layerswith different densities. As another example, two shunt BAW resonatorsof a filter can have patterned mass loading layers with differentdensities. As one more example, a series BAW resonator and shunt BAWresonator of a filter can have patterned mass loading layers withdifferent densities.

In some instances, two or more BAW resonators of a filter can havepatterned mass loading layer with the same density while one or moreother BAW resonators of the filter have patterned mass loading layerswith different densities. Such BAW resonators with patterned massloading layers with the same density can have a resonant frequency tunedby a same amount by respective patterned mass loading layers.

The patterned mass loading layer impacts the resonant frequency of a BAWresonator. Other layers of the BAW resonator also impact the resonantfrequency. Patterned mass loading layers with different densities canaccount for some or all of a difference in resonant frequency betweentwo BAW resonators. Differences in mass loading provided by one or moreother layers (e.g., one or more electrode layers and/or one or morepassivation layers) together with patterned mass loading layers withdifferent densities can cause BAW resonators to have different resonantfrequencies in certain applications. Alternatively, a difference indensity in patterned mass loading layers can account for an entiredifference in resonant frequency between BAW resonators in variousapplications.

Some methods of manufacturing BAW resonators involve multiple processsteps to make BAW resonators having different resonant frequencies. Alithography and etch process can be performed for each differentresonant frequency. Lithography and etch processes can be performed toform higher resonant frequencies. A lithography and deposition processcan be performed for each different resonant frequency. Lithography anddeposition processes can be performed to form lower resonantfrequencies. As BAW resonators with more different resonant frequenciesare included on a die, the number of process steps can increase. Withmore processing steps, manufacturing BAW resonators can become morecomplex and expensive.

Patterned mass loading layers having different densities can be formedin a common processing step. Accordingly, methods of manufacturing BAWresonators disclosed herein can reduce a number of processing steps toform BAW resonators having a plurality of different resonantfrequencies.

The common processing step can reduce process complexity and cost ofmanufacturing BAW resonators. By using a common processing step tomodify resonant frequency of a plurality of different BAW resonators,resonant frequency can be adjusted using a common processing step and asingle parameter. Adjusting density of a mass loading layer between nofill and 100% fill can enable resonant frequency of a BAW resonator tobe tuned within a tuning range. This can provide flexibility in tuningresonant frequency within the tuning range with one photolithographyprocess step. The common processing step can be used for forming BAWresonators with different frequencies that are included in the samefilter. The common processing step can be used for forming BAWresonators with different frequencies that are included in two or morefilters on a shared die.

Patterned mass loading layers can be precisely manufactured.Photolithography techniques for manufacturing surface acoustic wave(SAW) devices can be applied to forming a patterned mass loading layerin certain applications. In some applications, patterned mass loadinglayers can be formed during processes for manufacturing SAW and BAWdevices on the same die. Methods disclosed herein can achieve accuratecontrol of the resonant frequency of each BAW resonator.

Patterned mass loading layers can include a strip line patterns. Thestrip patterns can have a pitch P<3 h, where h is the total thickness ofa resonator stack from a bottom side passivation over an acousticreflector (e.g., an air cavity or solid acoustic mirror) to a top sidepassivation. In certain applications, P<2.4 h is preferred. Thepatterned mass loading layer can have a thickness d, where h<1.5 h. Thepatterned mass loading layer can have a thickness d, where 0.001h<d<1.5h. In certain applications, d<0.3 h is preferred.

The patterned mass loading layer can have any suitable pattern, such asa periodic pattern, a gradient pattern, a pitched modulated pattern, ora random pattern. The patterned mass loading layer can be equivalent toan even mass loading distribution. In plan view, shapes of pattern caninclude stripe, grating, gradient, the like, or any suitable combinationthereof. In cross-sectional view, shapes of the pattern can include arectangle, a trapezoidal, lens, the like, or any suitable combinationthereof.

The patterned mass loading layer can be positioned over an acousticreflector (e.g., an air cavity or solid acoustic mirror) of a BAWdevice, in which the acoustic reflector is positioned between a supportsubstrate and a lower electrode of the BAW device. The patterned massloading layer can be located on top of a BAW device, between a topelectrode and a passivation, or in any other suitable position over anacoustic reflector, where the acoustic reflector is positioned between asupport substrate and a lower electrode of the BAW device. The massloading pattern can be located in at least a main acoustically activeregion of a BAW device. In certain applications, the mass loadingpattern can be in a recessed frame region. In such applications, themass loading pattern can have a lower density in the recessed frameregion than in the main acoustically active region.

The patterned mass loading layer can include any suitable material sucha dielectric, a metal, a metal alloy, or any suitable combinationthereof. Patterned mass loading layers of denser materials can changeresonant frequency by more than less dense patterned mass loading layersfor the same change in duty factor. Patterned mass loading layers ofdenser materials can adjust resonant frequency with smaller changes induty factor compared to less dense patterned mass loading layers. Thepatterned mass loading layer can include a dielectric layer, such assilicon dioxide (SiO₂), silicon nitride (SiN), aluminum oxide (Al₂O₃),silicon carbide (SiC), aluminum nitride (AlN), titanium nitride (TiN),silicon oxynitride (SiON), or diamond like carbon (DLC). The patternedmass loading layer can include a metal layer, such as titanium (Ti),ruthenium (Ru), molybdenum (Mo), tungsten (W), platinum (Pt), aluminum(Al), iridium (Ir), chromium (Cr), cobalt (Co), nickel (Ni), copper(Cu), gold (Au), or any suitable alloy thereof.

Example BAW resonators with patterned mass loading layers will now bediscussed. Any suitable principles and advantages of these BAWresonators can be implemented together with each other. Althoughembodiments disclosed herein include a single patterned mass loadinglayer, any suitable principles and advantages disclosed herein can beapplied to a BAW resonator with two or more patterned mass loadinglayers. In applications with two or more patterned mass loading layers,the mass loading layers can have different patterns or the samepatterns.

FIG. 1A is a schematic cross-sectional diagram of a BAW resonator 10according to an embodiment. The BAW resonator 10 includes a patternedmass loading layer. The patterned mass loading layer impacts theresonant frequency of the BAW resonator 10. The BAW resonator 10 is afilm bulk acoustic wave resonator (FBAR). As illustrated, the BAWresonator 10 includes a support substrate, an air cavity 12, a recessedframe structure 13, a raised frame structure 14, a material stack 15 inan active region, and an electrical interconnect layer 16. The materialstack 15 includes the patterned mass loading layer. More details aboutthe material stack 15 will be discussed below with reference to FIG. 2.

An active region or active domain of the BAW resonator 10 can be definedby a portion of a piezoelectric layer of the material stack 15 that isin contact with both a lower electrode and an upper electrode andoverlaps an acoustic reflector, such as the air cavity 12 or a solidacoustic mirror. In applications where there are a plurality ofpiezoelectric layers of a BAW device, the active region can be definedby piezoelectric material of the piezoelectric layers being in contactwith both a lower electrode and an upper electrode over an acousticreflector. The active region corresponds to where voltage is applied onopposing sides of the piezoelectric layer over the acoustic reflector.The active region can be the acoustically active region of the BAWresonator 10. The BAW resonator 10 also includes a recessed frame regionwith the recessed frame structure 13 in the active region and a raisedframe region with the raised frame structure 14 in the active region.Acoustic activity can be reduced significantly in the recessed frameregion and the raised frame region. A main acoustically active regioncan be the central part of the active region that is free from framestructures 13 and 14. The main resonant frequency of the BAW resonator10 can be set by the main acoustically active region.

While FIG. 1A includes a recessed frame structure 13 and a raised framestructure 14, other frame structures can alternatively or additionallybe implemented. For example, a raised frame structure with multiplelayers including a layer between an electrode of a BAW resonator and apiezoelectric layer can be implemented. As another example, a raisedframe structure can include a layer embedded in piezoelectric material.As another example, a floating raised frame structure can beimplemented. As one more example, a raised frame structure can beimplemented without a recessed frame structure in a frame zone.

The air cavity 12 is an example of an acoustic reflector. Asillustrated, the air cavity 12 is located above the support substrate11. The air cavity 12 is positioned between the support substrate 11 andthe material stack 15. In some other embodiments, an air cavity can beetched into a support substrate. The support substrate 11 can be asilicon substrate. The support substrate 11 can be any other suitablesupport substrate. The electrical interconnect layer 16 can electricallyconnect electrodes of the BAW resonator 10 one or more other BAWresonators, one or more other circuit elements, one or more signalports, the like, or any suitable combination thereof.

FIG. 1B is an example plan view of the BAW resonator 10 of FIG. 1A. Thecross-sectional view of FIG. 1A is along the line from A to A′ in FIG.1B. As shown in FIG. 1B, the BAW resonator 10 includes a frame zone 17around the perimeter of a main acoustically active region 18 of the BAWresonator 10. The frame zone 17 can include the recessed frame structure13 and the raised frame structure 14 of FIG. 1A. The frame zone 17 canbe referred to as a border ring in certain instances. The material stack15 can extend further above a piezoelectric layer 19 in a raised frameregion than in the main acoustically active area 18 and the materialstack 15 can extend further above the piezoelectric layer 19 in the mainacoustically active area 18 than in the recessed frame region. FIG. 1Billustrates the BAW resonator 10 with a semi-elliptical shape in planview.

FIG. 1C is another example plan view of the BAW resonator 10 of FIG. 1A.The cross-sectional view of FIG. 1A is along the line from A to A′ inFIG. 1C. FIG. 1C illustrates the BAW resonator 10 with a pentagon shapedwith curved sides in plan view.

In some other embodiments, a BAW resonator in accordance with anysuitable principles and advantages disclosed herein can have any othersuitable shape in plan view, such as a quadrilateral shape, aquadrilateral shape with curved sides, a pentagon shape, a semi-circularshape, a circular shape, ellipsoid shape, or the like.

FIG. 2 includes a schematic cross-sectional view of the material stack15 of the BAW resonator 10 of FIG. 1A. FIG. 2 also illustrates apatterned mass loading layer 25 in plan view. The material stack 15 islocated in the main acoustically active region of the BAW resonator 10.The material stack 15 is positioned over the air cavity 12 in FIG. 1A.The material stack 15 can be positioned over any other suitable acousticreflector, such as a solid acoustic mirror, in another BAW resonator. Asillustrated, the material stack 15 includes a first passivation layer21, a first electrode layer 22, a piezoelectric layer 19, a secondelectrode layer 23, a second passivation layer 24, and a patterned massloading layer 25.

In the material stack 15, the piezoelectric layer 19 is positionedbetween the first electrode layer and the second electrode layer 23. Asillustrated, the piezoelectric layer 19 is physical contact withrespective planar surfaces of the first electrode layer 22 and thesecond electrode layer 24. The piezoelectric layer 19 can be an aluminumnitride layer. The piezoelectric layer 19 can be a zinc oxide layer. Thepiezoelectric layer 19 can include any suitable piezoelectric material.The piezoelectric layer 19 can be doped with any suitable dopant, suchas scandium (Sc), chromium (Cr), magnesium (Mg), or the like. Doping thepiezoelectric layer 19 can adjust resonant frequency. Doping thepiezoelectric layer 19 can increase the coupling coefficient k² of theBAW device 10. Doping to increase the coupling coefficient k² can beadvantageous at higher frequencies where the coupling coefficient k² canbe degraded.

The first passivation layer 21 is positioned between an acousticreflector and the first electrode layer 22. The first passivation layer21 can be referred to as a lower passivation layer. The firstpassivation layer 21 can be a silicon dioxide layer or any othersuitable passivation layer, such as aluminum oxide, silicon carbide,aluminum nitride, silicon nitride, silicon oxynitride, or the like. Asshown in FIG. 1A (although not shown in FIG. 2), there can be anadhesion layer, such as a titanium layer, positioned between the firstpassivation layer 21 and the first electrode layer 22.

The first electrode layer 22 can be referred to as a lower electrode.The first electrode layer 22 can have a relatively high acousticimpedance. The first electrode layer 22 can include molybdenum (Mo),tungsten (W), ruthenium (Ru), chromium (Cr), iridium (Ir), platinum(Pt), Ir/Pt, or any suitable alloy and/or combination thereof.Similarly, the second electrode layer 23 can have a relatively highacoustic impedance. The second electrode layer 23 can include Mo, W, Ru,Cr, Ir, Pt, Ir/Pt, or any suitable alloy and/or combination thereof. Thesecond electrode layer 23 can be formed of the same material as thefirst electrode layer 22 in certain instances. The second electrodelayer 23 can be referred to as an upper electrode. The piezoelectriclayer 19 is positioned between the first and second electrode layers 22and 23, respectively.

The second passivation layer 24 can be referred to as an upperpassivation layer. The second passivation layer 24 can be a silicondioxide layer or any other suitable passivation layer, such as aluminumoxide, silicon carbide, aluminum nitride, silicon nitride, siliconoxynitride, or the like. The second passivation layer 24 can be the samematerial as the first passivation layer 21 in certain instances.

In the material stack 15, the patterned mass loading layer 25 is formedover and in physical contact with the second passivation layer 24. Thepatterned mass loading layer 25 and the second passivation layer 24 areformed of the same material in the material stack 15. The patterned massloading layer 25 can be a silicon dioxide layer or any other suitablepassivation layer, such as aluminum oxide, silicon carbide, aluminumnitride, silicon nitride, silicon oxynitride, or the like.

The patterned mass loading layer 25 can include a plurality of stripsspaced apart from each other in a periodic pattern. The patterned massloading layer 25 has a height d and a pitch P. The pitch P and height dimpact mass loading of the BAW resonator 10 a central area of the activeregion, which in turn impacts resonant frequency of the BAW resonator10. By adjusting the pitch P, the density of the pass loading layer 25is adjusted. A smaller pitch P can result in a higher density and lowerresonant frequency. Similarly, a larger pitch P can result in a smallerdensity and higher resonant frequency. Adjusting the height d canalternatively or additionally adjust the mass loading of the patternedmass loading layer 25.

As illustrated, the patterned mass loading layer can have periodicpattern. The periodic pattern can have a duty factor where the dutyfactor is defined by the width of a strip divided by the pitch. The dutyfactor can be from 0 (no mass loading layer) to 1 (full mass loadinglayer). Different BAW resonators can have different duty factors toadjust resonant frequency. More generally, a duty factor can correspondto a fill percentage or pattern density of the mass loading layer overan area of a BAW device. For example, a patterned mass loading layer ina main acoustically active region of a BAW device has a duty factor of0.2 for the main acoustically active region when 20% of the mainacoustically active region includes material of the patterned massloading layer. As another example, a patterned mass loading layer in amain acoustically active region of a BAW device has a duty factor of 0.7for the main acoustically active region when 70% of the mainacoustically active region includes material of the patterned massloading layer. Different regions of a BAW device can have different dutyfactors. For instances, in some embodiments, a patterned mass loadinglayer can have a lower duty factor in a recessed frame region of a BAWdevice than in a main acoustically active region of the BAW device.

The patterned mass loading layer 25 can be formed in the same processingstep as one or more other patterned mass loading layers of differentrespective BAW resonators that have different respective densities. Thedifferent BAW resonators can be include in the same filter as the BAWresonator 10 and/or in one or more different filters than the BAWresonator 10. The patterned mass loading layer 25 can be formed bylithography and deposition. The patterned mass loading layer 25 can beformed by lithography and etching. Lithographic techniques used formanufacturing surface acoustic wave devices can be used to form thepatterned mass loading layer.

Other embodiments of material stacks of BAW resonators with a patternedmass loading layer will be discussed with reference to example crosssections shown in FIGS. 3 to 14. These materials stacks can beimplemented in place of the material stack 15 of FIGS. 1A and/or 2. Anysuitable combination of features of material stacks of FIGS. 2 to 14 canbe combined with each other. The example material stacks of FIGS. 3 to14 include a patterned mass loading layer in a different position and/orof a different material than the patterned mass loading layer 25 of FIG.2. Any suitable manufacturing techniques and/or advantages can beimplemented for the material stacks of FIGS. 3 to 14 relative to thematerial stack 15 of FIG. 2. While a single patterned mass loading layeris shown in example embodiments, two or more patterned mass loadinglayers can be implemented in a single BAW resonator in someapplications. The patterned mass loading layers in FIGS. 2 to 14 can bein a main acoustically active region of a BAW resonator.

FIG. 3 includes a schematic cross-sectional view of a material stack 30of a BAW resonator. FIG. 3 also illustrates a patterned mass loadinglayer 35 in plan view with passivation material included betweenfeatures of the patterned mass loading layer 35. The material stack 30can be implemented in a central area of an active region of a BAWresonator. The material stack 30 is like the material stack 15 of FIG.2, except that (1) the material stack 30 includes a patterned massloading layer 35 in a different position and of a different materialthan the patterned mass loading layer 25 of FIGS. 2 and (2) the materialstack 30 also includes a second passivation layer 34 having a differentgeometry than the second passivation layer 24 of FIG. 2.

In FIG. 3, the patterned mass loading layer 35 is positioned over thesecond electrode layer 23. The second passivation layer 34 is over thepatterned mass loading layer. The patterned mass loading layer 35 isformed of a different material than the second electrode layer 23. Thepatterned mass loading layer 35 is also formed of a different materialthan the second passivation layer 34. The patterned mass loading layer35 can be formed of any suitable mass loading material. The patternedmass loading 35 layer can include a dielectric material and/or a metal.The patterned mass loading layer 35 include one or more of SiO2, SiN,Al₂O₃, SiC, Ti, Ru, Mo, or Al, and the second electrode layer 23 and thesecond passivation layer 34 are both formed of different material thanthe patterned mass loading layer 35. The density of the material of thepatterned mass loading layer 35 can be higher than the density of thematerial of the second passivation layer 34. In certain applications,the density of the material of the patterned mass loading layer 35 canbe higher than the density of the material of the second electrode layer23. The patterned mass loading layer 35 can cause the second passivationlayer 34 to have a different geometry than the passivation layer 24 ofFIG. 2.

FIG. 4 includes a schematic cross-sectional view of a material stack 40of a BAW resonator. FIG. 4 also illustrates a patterned mass loadinglayer 45 in plan view. The material stack 40 can be implemented in acentral area of an active region of a BAW resonator. The material stack40 is like the material stack 30 of FIG. 3, except that a patterned massloading layer 45 includes the same material as the second electrodelayer 23 in the material stack 40. The patterned mass loading layer 45can function as part of the upper electrode in the material stack 40.

FIG. 5 includes a schematic cross-sectional view of a material stack 50of a BAW resonator. The material stack 50 can be implemented in acentral area of an active region of a BAW resonator. The material stack50 is like the material stack 40 of FIG. 4, except that a patterned massloading layer 55 is located in a different position. The patterned massloading layer 55 is positioned between the piezoelectric layer 18 andthe first electrode layer 22. The patterned mass loading layer 55includes the same material as the first electrode layer 22. Thepatterned mass loading layer 55 can function as part of the lowerelectrode in the material stack 50.

FIG. 6 includes a schematic cross-sectional view of a material stack 60of a BAW resonator. The material stack 60 can be implemented in acentral area of an active region of a BAW resonator. The material stack60 is like the material stack 50 of FIG. 5, except that a patterned massloading layer 65 is located on an opposite side of the first electrodelayer 22 relative to the patterned mass loading layer 55. The patternedmass loading layer 65 is positioned between the first passivation layer21 and the first electrode layer 22. The patterned mass loading layer 65includes the same material as the first electrode. The patterned massloading layer 65 can function as part of the lower electrode in thematerial stack 60.

FIG. 7 includes a schematic cross-sectional view of a material stack 70of a BAW resonator. The material stack 70 can be implemented in acentral area of an active region of a BAW resonator. In the materialstack 70, a patterned mass loading layer 75 is positioned below thefirst passivation layer 21 and includes the same material as the firstpassivation layer 21. The patterned mass loading layer 75 is locatedbetween an acoustic reflector and the first passivation layer 21. Thepatterned mass loading layer 75 can be patterned over a sacrificiallayer that is later removed to from an air cavity below the patternedmass loading layer 75 in certain applications.

In certain embodiments, a patterned mass loading layer can be of amaterial different than any other layer(s) of a BAW material stack thatare in physical contact with the patterned mass loading layer. Suchpatterned mass loading layers can include any suitable dielectric and/ormetal. For example, such a patterned mass loading can include one ormore of SiO2, SiN, Al₂O₃, SiC, Ti, Ru, Mo, or Al, and any other layer(s)in contact with the patterned mass loading layer are of a differentmaterial. FIGS. 8 to 10 illustrate embodiments similar to certainembodiments discussed above, except where a patterned mass loading layerof a different material is included in place of a patterned mass loadinglayer of the same material as another layer in physical contact with thepatterned mass loading layer. FIGS. 11 to 14 illustrate embodimentswhere a patterned mass loading layer is embedded in another layer of aBAW material stack of a different material.

FIG. 8 includes a schematic cross-sectional view of a material stack 80of a BAW resonator. The material stack 80 is like the material stack 15of FIG. 2, except that a patterned mass loading layer 85 of a differentmaterial than the second passivation layer 24 is included in place ofthe patterned mass loading layer 25.

FIG. 9 includes a schematic cross-sectional view of a material stack 90of a BAW resonator. The material stack 90 is like the material stack 70of FIG. 7, except that a patterned mass loading layer 95 of a differentmaterial than the first passivation layer 21 is included in place of thepatterned mass loading layer 75.

FIG. 10 includes a schematic cross-sectional view of a material stack100 of a BAW resonator. The material stack 100 is like the materialstack 60 of FIG. 6, except that a patterned mass loading layer 105 of adifferent material than the first electrode layer 22 is included inplace of the patterned mass loading layer 65. The patterned mass loadinglayer 105 is also of a different material than the first passivationlayer 21.

FIG. 11 includes a schematic cross-sectional view of a material stack110 of a BAW resonator. In the material stack 110, a patterned massloading layer 115 is embedded in the second passivation layer 24. Thepatterned mass loading layer 115 is of a different material than thesecond passivation layer 24. The pattern mass loading layer 115 can havea higher density than the second passivation layer 24.

FIG. 12 includes a schematic cross-sectional view of a material stack120 of a BAW resonator. In the material stack 120, a patterned massloading layer 125 is embedded in the first passivation layer 21. Thepatterned mass loading layer 125 is of a different material than thefirst passivation layer 21. The pattern mass loading layer 125 can havea higher density than the first passivation layer 21.

FIG. 13 includes a schematic cross-sectional view of a material stack130 of a BAW resonator. In the material stack 130, a patterned massloading layer 135 is embedded in the second electrode layer 23. Thepatterned mass loading layer 135 is of a different material than thesecond electrode layer 23. The pattern mass loading layer 135 can have ahigher density than the second electrode layer 23.

FIG. 14 includes a schematic cross-sectional view of a material stack140 of a BAW resonator. In the material stack 140, a patterned massloading layer 145 is embedded in the first electrode layer 22. Thepatterned mass loading layer 145 is of a different material than thefirst electrode layer 22. The pattern mass loading layer 145 can have ahigher density than the first electrode layer 22.

Patterned mass loading layers can include features with a variety ofdifferent cross-sectional shapes. A patterned mass loading layer caninclude gratings spaced apart from each other. The gratings can have anysuitable cross-sectional shape, such as any of the cross-sectionalshapes shown in any of FIGS. 15B to 15H. FIG. 15A includes across-sectional view of the BAW material stack 30 of FIG. 3 and a planview of the patterned mass loading layer 35 for illustrative purposes.The cross-sectional shapes shown in of FIGS. 15B to 15H are exampleshapes for gratings of the patterned mass loading layer 35. Thecross-sectional shapes shown in any of FIGS. 15B to 15H can be includedin a patterned mass loading layer in accordance with any suitableprinciples and advantages disclosed herein. In certain embodiments, allgratings of a pattered mass loading layer can have the same shape incross-sectional view. In some other embodiments, gratings of a patternedmass loading layer can have two or more different shapes.

FIG. 15B illustrates a schematic cross-sectional view of a rectangulargrating 155B. Certain illustrated embodiments herein have rectangularshaped gratings. FIG. 15C illustrates a schematic cross-sectional viewof a trapezoidal grating 155C. FIG. 15D illustrates a schematiccross-sectional view of a triangular grating 155D. The triangulargrating 155 is symmetric in the cross-sectional view. FIG. 15Eillustrates a schematic cross-sectional view of a half ellipse shapedgrating 155E. The grating 155E can be referred to as a lens shapedgrating. A semicircular shaped grating can be implemented. FIG. 15Fillustrates a schematic cross-sectional view of a grating 155F with onetapered side and one flat side. FIG. 15G illustrates a schematiccross-sectional view of an asymmetrical triangular grating 155G. Thesides of the triangular grating 155 have different slopes. FIG. 15Hillustrates a schematic cross-sectional view of an asymmetrical lensshaped grating 155H.

Patterned mass loading layers can include any suitable pattern in planview. Example patterns include line patterns, loop patterns, crossedline patterns, random patterns, and the like. The density of features ofsuch patterns of a patterned mass loading layer can be adjusted tothereby adjust mass loading of the patterned mass loading layer. Examplepatterns shown in plan view are illustrated in FIGS. 16A to 19C. Thepatterns shown in these figures can be implemented with differentspacings between features to adjust mass loading. The patterns shown inany of FIGS. 16A to 19C can be implemented in a patterned mass loadinglayer in accordance with any suitable principles and advantagesdisclosed herein.

FIGS. 16A to 16C illustrate example patterned mass loading layers withline patterns in plan view. FIG. 16A shows a plan view of a patternedmass loading layer 160 that includes a plurality of line shaped features161 spaced apart from each other. FIG. 16B shows a plan view of apatterned mass loading layer 162 that includes a plurality of angledline shaped features 163 spaced apart from each other. FIG. 16C shows aplan view of a patterned mass loading layer 164 that includes aplurality of angled line shaped features 165 spaced apart from eachother, in which the angle is different than in the patterned massloading layer 162. These figures illustrate that features of thepatterned mass loading layer can be angled at any suitable angle α,where 0≤α≤180 degrees.

FIGS. 17A to 17D illustrate example patterned mass loading layers withloop patterns in plan view. These loop patterns include concentricshaped features of the patterned mass loading layer. FIG. 17A shows aplan view of a patterned mass loading layer 170 that includes aplurality of concentric rectangular shaped features 171 spaced apartfrom each other. As illustrated, the rectangular shaped features 171 aresquare shaped. FIG. 17B shows a plan view of a patterned mass loadinglayer 172 that includes a plurality of concentric pentagon shapedfeatures 173 spaced apart from each other. FIG. 17C shows a plan view ofa patterned mass loading layer 174 that includes a plurality ofconcentric circular features 175 spaced apart from each other. FIG. 17Dshows a plan view of a patterned mass loading layer 176 that includes aplurality of concentric ellipsoid features 177 spaced apart from eachother.

FIGS. 18A and 18B illustrate example patterned mass loading layers withcrossed line patterns in plan view. FIG. 18A shows a plan view of apatterned mass loading layer 180 that includes a plurality of firstlines 181 that intersect with a plurality of second lines 182. FIG. 18Bshows a plan view of a patterned mass loading layer 184 that includes aplurality of first lines 185 that intersect with a plurality of secondlines 186. In the patterned mass loading layers 180 and 184 the linesare angled differently. The lines of crossed line patterned mass loadinglayers can be at any suitable angle.

FIGS. 18C, 18D, and 18E illustrate other example patterned mass loadinglayers. FIG. 18C illustrates a patterned mass loading layer 187 withrectangular island features. The rectangular island features can besquared island features as illustrated. Any other suitable islandfeatures can be implemented in a patterned mass loading layer, such asother polygon island features, ellipsoid features, dot features, or thelike. FIG. 18D illustrates a patterned mass loading layer 188 with dotfeatures. FIG. 18E illustrates a patterned mass loading layer 189 withholes.

Patterned mass loading layers can have a plurality of different featuretypes in plan view. Including continuous features, dashed features,angled features, zig-zag features, or the like. FIGS. 19A to 19Cillustrate example patterned mass loading layers with different featurestypes for line patterns in plan view. These feature types can be appliedto any other suitable patterns. FIG. 19A shows a plan view of apatterned mass loading layer 190 that includes a plurality of continuousline features 191. FIG. 19B shows a plan view of a patterned massloading layer 192 that includes a plurality of dashed line features 193.FIG. 19C shows a plan view of a patterned mass loading layer 194 thatincludes a plurality of zig-zag line features 195.

FIG. 20A shows a plan view of a patterned mass loading layer 190 thatincludes a plurality of line features 191 over an underlying layer 192.FIG. 20B shows a side view of the line features 191 of the patternedmass loading layer and the underlying layer. The line features 191 allhave height d. The i-th line feature has a width ai. Each line featurecan have the same width a in certain embodiments. The line features 191have a period P. The period P can be constant for the line features. Insome instances, the spacing between adjacent features can change andpitch can be modulated. For example, there can be a gradient in spacingbetween line features 191 of the patterned mass loading layers.

Mass loading can depend on material of the line features 191, height ofthe line features 191, and pattern density/duty factor of the linefeatures 191.

The line features 191 can include any suitable mass loading material.The mass loading material can be a dielectric and/or passivationmaterial, such as SiO₂, SiN, Al₂O₃, SiC, AlN, or TiN. The mass loadingmaterial can be a metal layer, such as Ti, Ru, Mo, W, Pt, Al, Ir, Cr, orany suitable alloy thereof.

The line features can have a height d of less than 250 nanometers (nm)and greater than a minimum height for manufacturing. The height d can bein a range from about 10 nm to about 220 nm in certain applications. Theheight d can be in a range from about 20 nm to about 100 nm in someapplications. The height d can be in a range from about 20 nm to about50 nm in some applications. The line features have a height d in a rangefrom 0.001 h<d<1.5 h, where h is the total thickness of a resonatorstack from a bottom side passivation over an acoustic reflector (e.g.,air cavity or solid acoustic mirror) to a top side passivation. Incertain applications, d<0.3 h is preferred

The pitch P can be less than 3 h, where h is the total thickness of aresonator stack. In certain applications, P<2.4 h is preferred. Pitch Pcan be in a range from 0.2 micrometer to 2 micrometer in someapplications. Pitch P can be in a range from 0.2 micrometer to 1micrometer in various applications. Pitch P can be less than 1micrometer in certain applications.

The line features can have a pattern density from 0 to 100%. In certainapplications, a plurality of BAW resonators of a filter can have a dutyfactor in a range from 0.05 to 0.95 in a central region of an activearea, in which the duty factor is defined by the width of a line featurea divided by the pitch P. In some such instances, a plurality of BAWresonators of a filter can have a duty factor in a range from 0.2 to0.8. In some applications, a plurality of BAW resonators of a filter canhave a duty factor in a range from 0.3 to 0.7 in a central region of anactive area. A duty factor of a patterned mass loading layer in a mainacoustically active region of a BAW resonator in a range from 0.3 to 0.7can be desirable for a variety of applications. Duty factor canrepresent a ratio of an area that is covered by the patterned massloading layer. BAW devices with higher duty factor and high Qp valuescan be less sensitive to thickness and pitch length variation in certainapplications.

By adjusting pattern density for a particular mass loading material witha particular material height, resonant frequency of a BAW resonator canbe adjusted. Adjusting from a duty factor of 0 to a duty factor of 1 canchange a resonant frequency of a BAW resonator by an amount in a rangefrom about 0.5% to about 10% of a resonant frequency of the BAWresonator. Two BAW resonators with patterned mass loading layers withdifferent densities formed in the same processing step can have resonantfrequencies that are different by an amount in a range from about 0.1%to about 10% of the lower resonant frequency. In certain applications,the two BAW resonators with patterned mass loading layers with differentdensities formed in the same processing step can have resonantfrequencies that are different by an amount in a range from about 1% toabout 10%. In some applications, the two BAW resonators with patternedmass loading layers with different densities formed in the sameprocessing step can have resonant frequencies that are different by anamount in a range from about 1% to about 5%.

Resonant frequency variation among BAW devices on a common die can beachieved entirely by adjusting density of patterned mass loading layersin certain applications. Resonant frequency variation among BAW deviceson a common die can be achieved by adjusting density of patterned massloading layers combined with other techniques in some otherapplications.

FIG. 20C is a graph of simulation results for the patterned mass loadinglayer of FIGS. 20A and 20B. In these simulations, SiO₂ was used for apatterned mass loading layer and Ru was used for both electrodes. Thesimulation results in FIG. 20C indicate that changing from a duty factorof 0.3 to a duty factor of 0.7 for a particular thickness of thepatterned mass loading layer can adjust resonant frequency by 40 MHz. Incertain instances, patterned mass loading layers with a thickness ofless than 200 nm can be desirable. Thicker patterned mass loading layerscan have a greater impact in changing resonant frequency for the sameduty factor difference.

A BAW resonator with a patterned mass loading layer can be included inany suitable filter. The filter can be used to filter a radio frequencysignal. The filter can include a plurality of BAW resonators, one ormore BAW resonators and one or more other types of acoustic resonators,one or more BAW resonators and an inductor capacitor (LC) circuit, thelike or any suitable combination thereof. The filter can be any suitabletype of filter, such as band pass filter or a band rejection filter.Band pass filter can be implemented in applications for passing aparticular frequency band and rejecting frequencies outside of theparticular frequency band. The filter can have any suitable topology,such as a ladder topology, lattice topology, hybrid ladder latticetopology, or the like. An example ladder filter of BAW resonators withdifferent patterned mass loading layers will be described with referenceto FIG. 21.

FIG. 21 is a schematic diagram of a ladder filter 210 that includes aplurality of BAW resonators 211 to 219. As illustrated, the ladderfilter 210 includes series BAW resonators 211 to 215 and shunt BAWresonators 216 to 219. The BAW resonators 211 to 219 of the ladderfilter 210 have 7 different resonant frequencies. The series resonatorshave 4 resonant frequencies: BAW resonators 211 and 211 have resonantfrequency F1, BAW resonator 213 has resonant frequency F2, BAW resonator214 has resonant frequency F3, and BAW resonator 215 has resonantfrequency F4, where F1>F2>F3>F4. The shunt resonators have 3 resonantfrequencies: BAW resonators 216 and 217 have resonant frequency F5, BAWresonator 218 has resonant frequency F6, and BAW resonator 219 hasresonant frequency F7, where F5>F6>F7. F4 can be greater than F5. Theseexample resonant frequency relationships can be a for a band passfilter. For band pass filters, series resonators can provide an upperband edge of the frequency response and shunt resonators can provide alower band edge of the frequency response. In contrast, for bandrejection filters, series resonators can provide a lower band edge ofthe frequency response and shunt resonators can provide an upper bandedge of the frequency response. The relative resonant frequencyrelationships discussed above for F1 to F7 can be modified accordinglywhen applied to a band rejection filter.

In some existing methods, forming resonators with 7 different resonantfrequencies involves 6 different processing iterations. For example,there can be 6 iterations of depositing material on BAW resonatorstructures to provide BAW resonators with 7 different mass loadings thatwill result in 7 different resonant frequencies. As another example,there can be 6 iterations of etching material of BAW resonatorstructures to provide BAW resonators with 7 different mass loadings thatwill result in 7 different resonant frequencies.

Methods disclosed herein can create 7 resonant frequencies F1 to F7 witha common processing step. Patterned mass loading layers of different BAWresonators of the ladder filter 210 can be formed with a differentpattern density during the common processing step. This can adjust massloading of the BAW resonators with the different densities and result indifferent respective resonant frequencies. Such a method can beperformed to provide the BAW resonators of the ladder filter 210 with 7different resonant frequencies F1 to F7.

For example, the patterned mass loading layers of the BAW resonators ofthe ladder filter 210 can have strip line patterns. The strip linepatterns can be formed with different densities (e.g., differentpitches) in a common processing step to create different respectiveresonant frequencies. The different densities can be formed bydepositing material to form patterned mass loading layers. The differentdensities can be formed by etching material to form patterned massloading layers. In some instances, both deposition and etching can beperformed to provide mass loading for the BAW resonators of the ladderfilter 210. For instance, a common processing step could be performed toform patterned mass loading layers for the BAW resonators 211 to 219.Then an etching process can remove material between strips of thepatterned mass loading layers of the series BAW resonators 211 to 215 toreduce mass loading of the series BAW resonators 211 to 215 withoutimpacting mass loading of the shunt BAW resonators 216 to 219.

FIG. 22 is an example schematic cross-sectional diagram showing materialstacks of example BAW resonators of the ladder filter 210 of FIG. 21with different patterned mass loading layers. These different patternedmass loading layers can be formed in a common processing step. The BAWresonators illustrated in FIG. 22 have example patterned mass loadinglayers, although the principles and advantages of these resonators canbe implemented with any suitable patterned mass loading layers disclosedherein.

The BAW resonator 221 has a resonant frequency of F1. The BAW resonator221 does not include a patterned mass loading layer and can thus providea highest resonant frequency of the illustrated BAW resonators. The BAWresonator 221 can correspond to an example of BAW resonators 211 and 212of FIG. 21. The BAW resonator 222 has a resonant frequency of F2. TheBAW resonator 222 has a patterned mass loading layer 35 with lessdensity than corresponding patterned mass loading layers 35′ and 35″ ofBAW resonators 226 and 227, respectively. The BAW resonator 222 cancorrespond to an example of BAW resonator 213 of FIG. 21. The BAWresonator 226 has a resonant frequency of F6 and a patterned massloading layer 35′. The BAW resonator 226 can correspond to an example ofBAW resonator 218 of FIG. 21. The BAW resonator 227 has a resonantfrequency of F7 and a patterned mass loading layer 35″. The BAWresonator 226 can correspond to an example of BAW resonator 219 of FIG.21. The BAW resonator 227 has a maximum density where the patterned massloading layer 35″ has a 100% fill. The BAW resonator 227 can have alowest resonant frequency of the illustrated BAW resonators due tohaving the greatest mass loading. BAW resonators with resonantfrequencies of between F2 and F6 can be implemented with similarpatterned mass loading layers having densities between the densities ofthe patterned mass loading layers 35 and 35′, respectively.

FIGS. 23A and 23B are flow diagrams of example methods of forming BAWresonators with patterned mass loading layers. FIG. 23A relates to aprocess that involves liftoff where material is deposited over a BAWstructure to form patterned mass loading layers. FIG. 23B relates to aprocess that involves etching where material is removed to formpatterned mass loading layers. Any suitable combination of the featuresof the methods of FIGS. 23A and 23B can be combined with each other.

FIG. 23A is a flow diagram for a process 230 of manufacturing BAWresonators. The BAW resonators can be FBARs and/or BAW SMRs. The process230 includes providing a BAW resonator structure at block 232. The BAWresonator structure includes at least a support substrate. The BAWresonator structure can include one or more other layers over thesupport substrate. For example, the BAW resonator structure can includethe layers of a material stack below any of the patterned mass loadinglayers shown in any of FIGS. 2 to 14.

At block 234, material is deposited over the BAW resonator structure toform patterned mass loading layers during a common processing step. Thecommon processing step can form the patterned mass loading layersconcurrently. The common processing step can involve using a commonmask. During the common processing step, the material is deposited suchthat a first patterned mass loading layer is formed over the bulkacoustic wave resonator structure in a first area for a first bulkacoustic wave resonator and a second patterned mass loading layer overthe bulk acoustic wave resonator structure in a second area for a secondbulk acoustic wave resonator. The second patterned mass loading layerhas a different density than the first patterned mass loading layer. Anysuitable number of patterned mass loading layers can be formed fordifferent respective BAW resonators during the common processing step.These patterned mass loading layers can have any suitable number ofdifferent densities. For example, in the example of FIGS. 21 and 22, sixdensities of patterned mass loading layers can be formed to create sevendifferent resonant frequencies of BAW resonators.

During the common processing step at block 234, patterned mass loadinglayers can be formed for a plurality of BAW resonators of the samefilter. Alternatively or additionally, the common processing step caninvolve forming patterned mass loading layers of BAW resonators ofdifferent filters on the same die.

The patterned mass loading layer can be any of the patterned massloading layers of FIGS. 2 to 14. The patterned mass loading layer caninclude different material than a layer on which the patterned massloading layer is deposited. In addition, the patterned mass loadinglayer can include different material than a layer subsequently formedover the patterned mass loading layer. In some other embodiments, thepatterned mass loading layer can be of the same material as anunderlying or overlying layer.

FIG. 23B is a flow diagram for a process 235 of manufacturing BAWresonators. The BAW resonators can be FBARs and/or SMRs. The process 235includes providing a BAW resonator structure at block 236. The BAWresonator structure includes at least a support substrate. The BAWresonator structure can include one or more other layers over thesupport substrate. For example, the BAW resonator structure can includethe layers of a material stack below and including the patterned massloading layers (before patterning with 100% fill) shown in any of FIGS.2 to 14.

The patterned mass loading layer can be any of the patterned massloading layers of FIGS. 2 to 14. The patterned mass loading layer caninclude different material than a layer on which the patterned massloading layer is deposited. In addition, the patterned mass loadinglayer can include different material than a layer subsequently formedover the patterned mass loading layer. In some other embodiments, thepatterned mass loading layer can be of the same material as anunderlying or overlying layer.

At block 238, material is removed from the BAW resonator structure toform patterned mass loading layers during a common processing step. Thematerial can be etched such that a first patterned mass loading layer isformed on the bulk acoustic wave resonator structure in a first area fora first bulk acoustic wave resonator and a second patterned mass loadinglayer on the bulk acoustic wave resonator structure in a second area fora second bulk acoustic wave resonator. The second patterned mass loadinglayer has a different density than the first patterned mass loadinglayer. Any suitable number of patterned mass loading layers can beformed for different respective BAW resonators during the commonprocessing step at block 238. These patterned mass loading layers canhave any suitable number of different densities. For example, in theexample of FIGS. 21 and 22, six densities of patterned mass loadinglayers can be formed to create seven different resonant frequencies ofBAW resonators.

During the common processing step at block 238, patterned mass loadinglayers can be formed for a plurality of BAW resonators of the samefilter. Alternatively or additionally, the common processing step caninvolve forming patterned mass loading layers of BAW resonators ofdifferent filters on the same die.

The patterned mass loading layer can be any suitable patterned massloading layer of FIGS. 2 to 14. The patterned mass loading layer caninclude different material than a layer on which the patterned massloading layer is deposited. In addition, the patterned mass loadinglayer can include different material than a layer subsequently formedover the patterned mass loading layer. In some other embodiments, thepatterned mass loading layer can be of the same material as anunderlying and/or overlying layer.

FIGS. 24A and 24B illustrate different schematic cross sections ofmaterial stacks of BAW resonators corresponding to steps of theprocesses of FIGS. 23A and/or 23B. The illustrated BAW resonators can beincluded in the same filter. The illustrated BAW resonators can beincluded in two or more filters on the same die.

FIG. 24A illustrates three BAW structures 242, 244, and 246 with thesame material stacks. These BAW structures can correspond to the BAWstructures provided at block 232 of the process 230 and/or the BAWstructures provided at block 236 of the process 235.

FIG. 24B illustrates three BAW structures 242′, 244′, and 246′ withdifferent material stacks after a patterned mass loading layer isformed. The BAW structures 242′, 244′, and 246′ include respective massloading layers 25, 25′, and 25″ to provide different mass loading andimpact resonant frequency. These BAW structures can correspond to theBAW structures formed by depositing material at block 234 of the process230. Alternatively, these BAW structures can correspond to the BAWstructures formed by removing (e.g., etching) material at block 238 ofthe process 235.

FIG. 25 is a flow diagram for a process 250 of manufacturing BAWresonators. The BAW resonators can be FBARs and/or BAW SMRs. The process250 includes providing a BAW resonator structure at block 252. Patternedmass loading layers are formed for BAW resonators at block 254. This caninvolve depositing material and/or removing material. BAW resonators areinterconnected at block 256. The interconnecting can include connectingBAW resonators together as a filter. In some instances, interconnectingcan include connecting BAW resonators together as two or more filters.In some such instances, interconnecting can include connecting BAWresonators of the two or more filters together at a common node to forma multiplexer, such as a duplexer.

FIG. 26 is a top plan view schematically illustrating a BAW die 260 thatincludes BAW resonators with different patterned mass loading layers.BAW resonators of the BAW die 260 can be manufactured in accordance withany suitable principles and advantages disclosed herein. FIG. 26 showsview of material stacks of BAW resonators 266 and 268 of the BAW die260. The BAW resonators 266 and 268 have different patterned massloading layers with different densities that impact their respectiveresonant frequencies. The patterned mass loading layers of the BAWresonators 266 and 268 have periodic patterns. The periodic patternshave different duty factors. The patterned mass loading layers of theBAW resonators 266 and 268 each extend a same amount above an underlyinglayer. The BAW resonators 266 and 268 can be included in a singlefilter. The BAW resonators 266 and 268 can be included in differentfilters. The different filters can be included in a multiplexer, such asa duplexer. In certain embodiments, the BAW resonators 266 and 268 canhave the shape shown in FIG. 1B or the shape shown in FIG. 1C in planview.

FIG. 27 is a top plan view schematically illustrating a BAW die 270 thatincludes BAW resonators with different patterned mass loading layers.BAW resonators of the BAW die 270 can be manufactured in accordance withany suitable principles and advantages disclosed herein. FIG. 27 showsview of material stacks of BAW resonators 272, 274, and 276 of the BAWdie 270. The BAW resonators 272, 274, and 276 have different patternedmass loading layers with different densities that impact theirrespective resonant frequencies. The patterned mass loading layers ofthe BAW resonators 272, 274, and 276 have periodic patterns. Theperiodic patterns have different fill factors. The patterned massloading layers of the BAW resonators 272, 274, and 276 each extend asame amount above an underlying layer. The BAW resonators 272, 274, and276 can be included in a single filter. Any suitable number of BAWresonators with patterned mass loading layers can be included in asingle filter. The BAW resonators 272, 274, and 276 can be included intwo different filters. The two different filters can be included in amultiplexer, such as a duplexer. The BAW resonators 272, 274, and 276can be included in three different filters. The three different filterscan be included in a multiplexer, such as a triplexer. The principlesand advantages disclosed herein can be applied to manufacturing BAWresonators on a BAW die, in which the BAW resonators are included in anysuitable number of different filters of a multiplexer and/or anysuitable number of standalone filters. In certain embodiments, the BAWresonators 272, 274, and 276 can have the shape shown in FIG. 1B or theshape shown in FIG. 1C in plan view.

Patterned mass loading layers in accordance with any suitable advantagesdisclosed herein can be included in a variety of different acoustic wavedevices. Although some embodiments are disclosed in association withFBARs, any suitable features disclosed herein of such embodiments can beapplied to solidly mounted resonators (SMRs), Lamb wave resonators,plate wave resonators, oscillators with one or more acoustic resonators,or the like. An example of a BAW SMR with a patterned mass loading layerwill be discussed with reference to FIG. 28. In Lamb wave resonators, apatterned mass loading layer can be included above and/or below a lowerelectrode positioned between a piezoelectric layer and an acousticreflector.

FIG. 28 is a schematic cross-sectional diagram of a BAW SMR 280 with apatterned mass loading layer according to an embodiment. The BAW SMR 280is like the BAW resonator 10 of FIG. 1A except that a solid acousticmirror 285 is included in place of an air cavity 12. The solid acousticmirror 285 is an acoustic Bragg reflector. The solid acoustic mirror 285includes alternating low acoustic impedance and high acoustic impedancelayers. As one example, the solid acoustic mirror 285 can includealternating silicon dioxide layers as low impedance layers and tungstenlayers as high impedance layers. As illustrated, the BAW SMR 280includes material stack 15 with a patterned mass loading layer. Anyother material stacks and/or principles and advantages of patterned massloading layers disclosed herein can be applied in BAW SMRs.

Patterned mass loading layers can have different densities in mainacoustically active regions of different respective BAW resonators toadjust resonant frequency. A patterned mass loading layer can impactmass loading in a BAW device where mass loading is lower in a recessedframe region than in a main acoustically active region. Such a patternedmass loading layer can be implemented with any suitable principles andadvantages disclosed herein. A patterned mass loading layers can atleast contribute to a difference in mass loading between a mainacoustically active region of a BAW resonator and a recessed frameregion of the BAW resonator. A patterned mass loading layer can accountfor some or all of the difference in mass loading between the mainacoustically active region and the recessed frame region. For example, apatterned mass loading layer can account for an entire difference inmass loading between the main acoustically active region and therecessed frame region of a BAW resonator in certain applications. Asanother example, a patterned mass loading layer and one or more otherlayers can together account the difference in mass loading between themain acoustically active region and the recessed frame region of a BAWresonator in various applications. In both examples, the patterned massloading layer at least contributes to the difference in mass loading.

In certain embodiments, a patterned mass loading layer can be includedin both a main acoustically active region and a recessed frame region.In such embodiments, the patterned mass loading layer can have a higherdensity in the main acoustically active region than in a recessed frameregion. According to some embodiments, a patterned mass loading can beincluded in the main acoustically active region, and the recessed frameregion can be free from the patterned mass loading layer.

In a BAW resonator, a mass loading boundary between a main acousticallyactive region and a recessed frame region can be created in a variety ofdifferent ways. In some instances, this mass loading boundary can becreated by having a thinner upper passivation layer in the recessedframe region relative to the main acoustically active region. Exampleschematic cross-sectional views of BAW resonators with a thinner upperpassivation layer in a recessed frame region are shown in FIGS. 29A and29B. In certain applications, a patterned mass loading layer can createa mass loading boundary between a main acoustically active region and arecessed frame region. Example schematic cross-sectional views of BAWresonators with patterned mass loading layers providing more massloading in the main acoustically active region relative to the recessedframe region are shown in FIGS. 31A, 31B, and 31C. In these examples,the patterned mass loading layer includes the same material as an upperelectrode of a BAW resonator. In some other instances, a patterned massloading layer can include the same material as an upper passivationlayer (e.g., silicon dioxide) and the recessed frame region can haveless mass loading from the upper passivation layer (e.g., a thinnerupper passivation layer) and/or from the patterned mass loading layer(e.g., being free from the patterned mass loading layer or having alower density of the patterned mass loading layer than in the mainacoustically active region). Any suitable principles and advantages ofthe embodiments of FIGS. 29A to 32B can be implemented together witheach other. Any suitable principles and advantages of the embodiments ofFIGS. 29A to 32B can be implemented with one or more other features ofany other embodiments disclosed herein.

FIG. 29A is a schematic cross-sectional diagram of a main acousticallyactive region MAIN and a recessed frame region ReF of part of a BAWresonator 290 with a patterned mass loading layer 294. In FIG. 29A, anupper passivation layer 292, the patterned mass loading layer 294, andan upper electrode layer 296 are illustrated. Although not illustratedin FIG. 29A, the BAW device 290 can include a piezoelectric layer, alower electrode layer, a lower passivation, an acoustic reflector, and asupport substrate below the illustrated layers. The patterned massloading layer 294 includes the same material as the upper electrodelayer 296 in FIG. 29A. The patterned mass loading layer 294 is includedin both the recessed frame region ReF and the main acoustically activeregion MAIN in the BAW resonator 290. The upper passivation layer 292 isthinner in the recessed frame region ReF than in the main acousticallyactive region MAIN in the BAW resonator 290. This creates a differencein mass loading between the recessed frame region ReF and the mainacoustically active region MAIN.

FIG. 29B is a schematic cross-sectional diagram of a main acousticallyactive region and a recessed frame region of part of another BAWresonator 298 with a patterned mass loading layer 294. The BAW resonator298 is like the BAW resonator 290 of FIG. 29A, except that the upperpassivation layer 292′ in the BAW resonator 298 has a different geometrythan the upper passivation layer 292 of the BAW resonator 290. The upperpassivation layer 292′ has a geometry that is impacted by the patternedmass loading layer 294. In contrast, the upper passivation layer 292 ofFIG. 29A has planar upper surfaces.

FIG. 30 is flow diagram of an example method 300 of forming a BAWresonator with a patterned mass loading layer having a higher density ina main acoustically active region and a lower density in a raised frameregion according to an embodiment. The lower density of the patternedmass loading layer can provide a sufficient difference in mass loadingrelative to the main acoustically active region such that an upperpassivation can have substantially the same thickness over both the mainacoustically active region and the recessed frame region. In suchinstances, a recessed frame region can be realized without etching theupper passivation layer. This can eliminate a step of etching upperpassivation to create a recessed frame region from certain methods ofmanufacturing BAW resonators. The method 300 can create a recessed frameregion by including a patterned mass loading layer with a lower dutyfactor in a recessed frame region relative to a main acoustically activeregion, instead of a separate processing step to create the recessedframe region.

At block 302 of the method 300, a bulk acoustic wave resonator structureincluding a support substrate is provided. The bulk acoustic waveresonator structure can also include a passivation layer over thesupport substrate, an electrode layer over the passivation layer, and apiezoelectric layer over the electrode layer. In some applications, thebulk acoustic wave resonator structure can further include a secondelectrode over the piezoelectric layer.

At block 304 of the method 300, a common processing step is performed toform a patterned mass loading layer on the bulk acoustic wave resonatorstructure with a lower density in an area corresponding to a recessedframe region of a bulk acoustic wave resonator and a higher density inan area corresponding to a main acoustically active region of the bulkacoustic wave resonator. The common processing step can includedepositing material to form the patterned mass loading layer. The commonprocessing step can alternatively or additionally include removingmaterial to from the patterned mass loading layer. In certainapplications, the patterned mass loading layer can have a duty factor of0.3 or less in the area corresponding to the recessed frame region. Forexample, the duty factor in the area corresponding to the recessed frameregion can be in a range from 0.05 to 0.3. In such applications thepatterned mass loading layer can have a duty factor in the areacorresponding to the main acoustically active region that is greaterthan the duty factor in the area corresponding to the recessed frameregion. For example, the duty factor in the area corresponding to themain acoustically active region can be in a range from 0.3 to 0.8.

The patterned mass loading layer can be implemented in accordance withany suitable principles and advantages disclosed herein. For example,the patterned mass loading layer can include a periodic pattern. Asanother example, the patterned mass loading layer can include aplurality of strips spaced apart from each other.

After forming the patterned mass loading layer, a passivation layer canbe formed over an upper electrode of the bulk acoustic wave resonatorwithout etching material of the upper passivation layer over therecessed frame region. This can advantageously remove a processing steprelative to some other methods of manufacturing BAW resonators. In suchembodiments, an upper passivation layer can have substantially the samethickness in both a main acoustically active region and a recessed frameregion.

FIG. 31A is a schematic cross-sectional diagram of part of a BAWresonator 310 with a patterned mass loading layer 294″ in a mainacoustically active region MAIN and a recessed frame region ReF withouta patterned mass loading layer. The upper passivation layer 292″ canhave a geometry that is impacted by the underlying patterned massloading layer 294″. By forming the patterned mass loading layer 294″ inthe main acoustically active region MAIN and not in the recessed frameregion ReF, the recessed frame region ReF can be formed without etchingor otherwise removing material of the upper passivation layer 292″. Thiscan eliminate a processing step of etching upper passivation in arecessed frame region relative to certain other methods of manufacturingBAW resonators.

FIG. 31B is a schematic cross-sectional diagram of part of a BAWresonator 312 with a patterned mass loading layer 294′″ with a higherdensity in a main acoustically active region MAIN than in a recessedframe region ReF. The BAW resonator 312 can be manufactured by themethod 300. The upper passivation layer 292′″ has a geometry impacted bythe underlying patterned mass loading layer 294′″. The upper passivationlayer 292′″ extends farther from an underlying piezoelectric layer overfeatures of the patterned mass loading layer 294′″ in both the mainacoustically active region MAIN and the recessed frame region ReF.

FIG. 31C is a schematic cross-sectional diagram of part of a BAWresonator 314 with a patterned mass loading layer 294″″ with a higherdensity in a main acoustically active region MAIN than in a recessedframe region ReF. The upper passivation layer 292″″ extends farther froman underlying piezoelectric layer over features of the patterned massloading layer 294′″ in the main acoustically active region MAIN but notin the recessed frame region ReF. The upper passivation layer 292″″ canbe planarized in the recessed frame region ReF. Alternatively, a planarupper passivation layer can be formed and a second patterned massloading layer of the same material as the upper passivation layer can beformed only over the main acoustically active region. This is oneexample of another layer in a recessed frame region providing less massloading in the recessed frame region relative to the main acousticallyactive region in combination with a patterned mass loading layerproviding less mass loading in the recessed frame region relative to themain acoustically active region.

FIG. 32A is a plan view of a BAW resonator 320 with a patterned massloading layer 322. In the BAW resonator 320, the patterned mass loadinglayer can provide similar or the same mass loading in a mainacoustically active region relative to a recessed frame region. Therecessed frame region can be created by one or more other layers in amaterial stack, such as an upper passivation layer being thinner in arecessed frame region relative to a main acoustically active region.

FIG. 32B is a plan view of a BAW resonator 325 with a patterned massloading layer 328 and a recessed frame region 329 without the patternedmass loading layer 328. The recessed frame region 329 surrounds an areaassociated with the patterned mass loading layer 328 in the BAWresonator 325. The recessed frame region 329 can have reduced massloading relative to the main acoustically active region of the BAWresonator 325 due to being free from the patterned mass loading layer328. Being free from the patterned mass loading layer 328 can accountfor some or all of the difference in mass loading relative to the mainacoustically active region.

The principles and advantages disclosed herein can be implemented in astandalone filter and/or in one or more filters in any suitablemultiplexer. Such filters can be any suitable topology discussed herein,such as any filter topology in accordance with any suitable principlesand advantages disclosed with reference to any of FIG. 21. The filtercan be a band pass filter arranged to filter a fourth generation (4G)Long Term Evolution (LTE) band and/or a fifth generation (5G) New Radio(NR) band. Examples of a standalone filter and multiplexers will bediscussed with reference to FIGS. 33A to 33E. Any suitable principlesand advantages of these filters and/or multiplexers can be implementedtogether with each other. Moreover, the anti-series bulk acoustic bulkacoustic wave resonators disclosed herein can be included in filter thatalso includes one or more inductors and one or more capacitors.

FIG. 33A is schematic diagram of an acoustic wave filter 330. Theacoustic wave filter 330 is a band pass filter. The acoustic wave filter330 is arranged to filter a radio frequency signal. The acoustic wavefilter 330 includes a plurality of acoustic wave resonators coupledbetween a first input/output port RF_IN and a second input/output portRF_OUT. The acoustic wave filter 330 includes one or more BAW resonatorswith a patterned mass loading layer implemented in accordance with anysuitable principles and advantages disclosed herein.

FIG. 33B is a schematic diagram of a duplexer 332 that includes anacoustic wave filter according to an embodiment. The duplexer 332includes a first filter 330A and a second filter 330B coupled totogether at a common node COM. One of the filters of the duplexer 332can be a transmit filter and the other of the filters of the duplexer332 can be a receive filter. In some other instances, such as in adiversity receive application, the duplexer 332 can include two receivefilters. Alternatively, the duplexer 332 can include two transmitfilters. The common node COM can be an antenna node.

The first filter 330A is an acoustic wave filter arranged to filter aradio frequency signal. The first filter 330A includes acoustic waveresonators coupled between a first radio frequency node RF1 and thecommon node COM. The first radio frequency node RF1 can be a transmitnode or a receive node. The first filter 330A includes one or more BAWresonators with a patterned mass loading layer implemented in accordancewith any suitable principles and advantages disclosed herein.

The second filter 330B can be any suitable filter arranged to filter asecond radio frequency signal. The second filter 330B can be, forexample, an acoustic wave filter, an acoustic wave filter that includesone or more BAW resonators with a patterned mass loading layerimplemented in accordance with any suitable principles and advantagesdisclosed herein, an LC filter, a hybrid acoustic wave LC filter, or thelike. The second filter 330B is coupled between a second radio frequencynode RF2 and the common node. The second radio frequency node RF2 can bea transmit node or a receive node.

Although example embodiments may be discussed with filters or duplexersfor illustrative purposes, any suitable principles and advantagesdisclosed herein can be implemented in a multiplexer that includes aplurality of filters coupled together at a common node. Examples ofmultiplexers include but are not limited to a duplexer with two filterscoupled together at a common node, a triplexer with three filterscoupled together at a common node, a quadplexer with four filterscoupled together at a common node, a hexaplexer with six filters coupledtogether at a common node, an octoplexer with eight filters coupledtogether at a common node, or the like. Multiplexers can include filtershaving different passbands. Multiplexers can include any suitable numberof transmit filters and any suitable number of receive filters. Forexample, a multiplexer can include all receive filters, all transmitfilters, or one or more transmit filters and one or more receivefilters. One or more filters of a multiplexer can include any suitablenumber of BAW resonators with a patterned mass loading layer.

FIG. 33C is a schematic diagram of a multiplexer 334 that includes anacoustic wave filter according to an embodiment. The multiplexer 334includes a plurality of filters 330A to 330N coupled together at acommon node COM. The plurality of filters can include any suitablenumber of filters including, for example, 3 filters, 4 filters, 5filters, 6 filters, 7 filters, 8 filters, or more filters. Some or allof the plurality of acoustic wave filters can be acoustic wave filters.As illustrated, the filters 330A to 330N each have a fixed electricalconnection to the common node COM. This can be referred to as hardmultiplexing or fixed multiplexing. Filters have fixed electricalconnections to the common node in hard multiplexing applications. Eachof the filters 330A to 330N has a respective input/output node RF1 toRFN.

The first filter 330A is an acoustic wave filter arranged to filter aradio frequency signal. The first filter 330A can include one or moreacoustic wave devices coupled between a first radio frequency node RF1and the common node COM. The first radio frequency node RF1 can be atransmit node or a receive node. The first filter 330A one or more BAWresonators with a patterned mass loading layer in accordance with anysuitable principles and advantages disclosed herein. The other filter(s)of the multiplexer 334 can include one or more acoustic wave filters,one or more acoustic wave filters that include one or more BAWresonators with a patterned mass loading layer, one or more LC filters,one or more hybrid acoustic wave LC filters, or any suitable combinationthereof.

FIG. 33D is a schematic diagram of a multiplexer 336 that includes anacoustic wave filter according to an embodiment. The multiplexer 336 islike the multiplexer 334 of FIG. 33C, except that the multiplexer 336implements switched multiplexing. In switched multiplexing, a filter iscoupled to a common node via a switch. In the multiplexer 336, theswitch 337A to 337N can selectively electrically connect respectivefilters 330A to 330N to the common node COM. For example, the switch337A can selectively electrically connect the first filter 330A thecommon node COM via the switch 337A. Any suitable number of the switches337A to 337N can electrically a respective filters 330A to 330N to thecommon node COM in a given state. Similarly, any suitable number of theswitches 337A to 337N can electrically isolate a respective filter 330Ato 330N to the common node COM in a given state. The functionality ofthe switches 337A to 337N can support various carrier aggregations.

FIG. 33E is a schematic diagram of a multiplexer 338 that includes anacoustic wave filter according to an embodiment. The multiplexer 338illustrates that a multiplexer can include any suitable combination ofhard multiplexed and switched multiplexed filters. One or more BAWresonators with a patterned mass loading layer can be included in afilter that is hard multiplexed to the common node of a multiplexer.Alternatively or additionally, one or more BAW resonators with apatterned mass loading layer can be included in a filter that is switchmultiplexed to the common node of a multiplexer.

The acoustic wave devices with a patterned mass loading layer disclosedherein can be implemented in a variety of packaged modules. Some examplepackaged modules will now be discussed in which any suitable principlesand advantages of the acoustic wave devices disclosed herein can beimplemented. The example packaged modules can include a package thatencloses the illustrated circuit elements. The illustrated circuitelements can be disposed on a common packaging substrate. The packagingsubstrate can be a laminate substrate, for example. FIGS. 34 to 38 areschematic block diagrams of illustrative packaged modules according tocertain embodiments. Any suitable combination of features of thesepackaged modules can be implemented with each other. While duplexers areillustrated in the example packaged modules of FIGS. 35 to 38, any othersuitable multiplexer that includes a plurality of filters coupled to acommon node can be implemented instead of one or more duplexers. Forexample, a quadplexer can be implemented in certain applications.Alternatively or additionally, one or more filters of a packaged modulecan be arranged as a transmit filter or a receive filter that is notincluded in a multiplexer.

FIG. 34 is a schematic diagram of a radio frequency module 340 thatincludes an acoustic wave component 342 according to an embodiment. Theillustrated radio frequency module 340 includes the acoustic wavecomponent 342 and other circuitry 343. The acoustic wave component 342can include one or more BAW resonators with a patterned mass loadinglayer in accordance with any suitable combination of features disclosedherein. The acoustic wave component 342 can include a BAW die thatincludes BAW resonators.

The acoustic wave component 342 shown in FIG. 34 includes a filter 344and terminals 345A and 345B. The filter 344 includes one or more BAWresonators implemented in accordance with any suitable principles andadvantages disclosed herein. The terminals 345A and 344B can serve, forexample, as an input contact and an output contact. The acoustic wavecomponent 342 and the other circuitry 343 are on a common packagingsubstrate 346 in FIG. 34. The package substrate 346 can be a laminatesubstrate. The terminals 345A and 345B can be electrically connected tocontacts 347A and 347B, respectively, on the packaging substrate 346 byway of electrical connectors 348A and 348B, respectively. The electricalconnectors 348A and 348B can be bumps or wire bonds, for example.

The other circuitry 343 can include any suitable additional circuitry.For example, the other circuitry can include one or more one or moreradio frequency amplifiers (e.g., one or more power amplifiers and/orone or more low noise amplifiers), one or more power amplifiers, one ormore radio frequency switches, one or more additional filters, one ormore low noise amplifiers, one or more RF couplers, one or more delaylines, one or more phase shifters, the like, or any suitable combinationthereof. The other circuitry 343 can be electrically connected to thefilter 344. The radio frequency module 340 can include one or morepackaging structures to, for example, provide protection and/orfacilitate easier handling of the radio frequency module 340. Such apackaging structure can include an overmold structure formed over thepackaging substrate 340. The overmold structure can encapsulate some orall of the components of the radio frequency module 340.

FIG. 35 is a schematic block diagram of a module 350 that includesduplexers 351A to 351N and an antenna switch 352. One or more filters ofthe duplexers 351A to 351N can include one or more BAW resonators with apatterned mass loading layer in accordance with any suitable principlesand advantages discussed herein. Any suitable number of duplexers 351Ato 351N can be implemented. The antenna switch 352 can have a number ofthrows corresponding to the number of duplexers 351A to 351N. Theantenna switch 352 can include one or more additional throws coupled toone or more filters external to the module 350 and/or coupled to othercircuitry. The antenna switch 352 can electrically couple a selectedduplexer to an antenna port of the module 350.

FIG. 36 is a schematic block diagram of a module 354 that includes apower amplifier 355, a radio frequency switch 356, and multiplexers 351Ato 351N in accordance with one or more embodiments. The power amplifier355 can amplify a radio frequency signal. The radio frequency switch 356can be a multi-throw radio frequency switch. The radio frequency switch356 can electrically couple an output of the power amplifier 355 to aselected transmit filter of the multiplexers 351A to 351N. One or morefilters of the multiplexers 351A to 351N can include any suitable numberof BAW resonators with a patterned mass loading layer in accordance withany suitable principles and advantages discussed herein. Any suitablenumber of multiplexers 351A to 351N can be implemented.

FIG. 37 is a schematic block diagram of a module 357 that includesmultiplexers 351A′ to 351N′, a radio frequency switch 358′, and a lownoise amplifier 359 according to an embodiment. One or more filters ofthe multiplexers 351A′ to 351N′ can include any suitable number BAWresonators with a patterned mass loading layer in accordance with anysuitable principles and advantages disclosed herein. Any suitable numberof multiplexers 351A′ to 351N′ can be implemented. The radio frequencyswitch 358 can be a multi-throw radio frequency switch. The radiofrequency switch 358 can electrically couple an output of a selectedfilter of multiplexers 351A′ to 351N′ to the low noise amplifier 359. Insome embodiments (not illustrated), a plurality of low noise amplifierscan be implemented. The module 357 can include diversity receivefeatures in certain applications.

FIG. 38 is a schematic diagram of a radio frequency module 380 thatincludes an acoustic wave filter according to an embodiment. Asillustrated, the radio frequency module 380 includes duplexers 382A to382N that include respective transmit filters 383A1 to 383N1 andrespective receive filters 383A2 to 383N2, a power amplifier 384, aselect switch 385, and an antenna switch 386. The radio frequency module380 can include a package that encloses the illustrated elements. Theillustrated elements can be disposed on a common packaging substrate387. The packaging substrate 387 can be a laminate substrate, forexample. A radio frequency module that includes a power amplifier can bereferred to as a power amplifier module. A radio frequency module caninclude a subset of the elements illustrated in FIG. 38 and/oradditional elements. The radio frequency module 380 may include one ormore BAW resonators with a patterned mass loading layer in accordancewith any suitable principles and advantages disclosed herein.

The duplexers 382A to 382N can each include two acoustic wave filterscoupled to a common node. For example, the two acoustic wave filters canbe a transmit filter and a receive filter. As illustrated, the transmitfilter and the receive filter can each be a band pass filter arranged tofilter a radio frequency signal. One or more of the transmit filters383A1 to 383N1 can include one or more BAW resonators with a patternedmass loading layer in accordance with any suitable principles andadvantages disclosed herein. Similarly, one or more of the receivefilters 383A2 to 383N2 can include one or more BAW resonators with apatterned mass loading layer in accordance with any suitable principlesand advantages disclosed herein. Although FIG. 38 illustrates duplexers,any suitable principles and advantages disclosed herein can beimplemented in other multiplexers (e.g., quadplexers, hexaplexers,octoplexers, etc.) and/or in switched multiplexers.

The power amplifier 384 can amplify a radio frequency signal. Theillustrated switch 385 is a multi-throw radio frequency switch. Theswitch 385 can electrically couple an output of the power amplifier 384to a selected transmit filter of the transmit filters 383A1 to 383N1. Insome instances, the switch 385 can electrically connect the output ofthe power amplifier 384 to more than one of the transmit filters 383A1to 383N1. The antenna switch 386 can selectively couple a signal fromone or more of the duplexers 382A to 382N to an antenna port ANT. Theduplexers 382A to 382N can be associated with different frequency bandsand/or different modes of operation (e.g., different power modes,different signaling modes, etc.).

BAW resonators with a patterned mass loading layer disclosed herein canbe implemented in a variety of wireless communication devices, such asmobile devices. FIG. 39 is a schematic diagram of one embodiment of amobile device 390. The mobile device 390 includes a baseband system 391,a transceiver 392, a front end system 393, antennas 394, a powermanagement system 395, a memory 396, a user interface 397, and a battery398.

The mobile device 390 can be used communicate using a wide variety ofcommunications technologies, including, but not limited to, secondgeneration (2G), third generation (3G), fourth generation (4G)(including LTE, LTE-Advanced, and LTE-Advanced Pro), fifth generation(5G) New Radio (NR), wireless local area network (WLAN) (for instance,WiFi), wireless personal area network (WPAN) (for instance, Bluetoothand ZigBee), WMAN (wireless metropolitan area network) (for instance,WiMax), Global Positioning System (GPS) technologies, or any suitablecombination thereof.

The transceiver 392 generates RF signals for transmission and processesincoming RF signals received from the antennas 394. It will beunderstood that various functionalities associated with the transmissionand receiving of RF signals can be achieved by one or more componentsthat are collectively represented in FIG. 39 as the transceiver 392. Inone example, separate components (for instance, separate circuits ordies) can be provided for handling certain types of RF signals.

The front end system 393 aids in conditioning signals transmitted toand/or received from the antennas 394. In the illustrated embodiment,the front end system 393 includes antenna tuning circuitry 400, poweramplifiers (PAs) 401, low noise amplifiers (LNAs) 402, filters 403,switches 404, and signal splitting/combining circuitry 405. However,other implementations are possible. One or more of the filters 403 canbe implemented in accordance with any suitable principles and advantagesdisclosed herein. For example, one or more of the filters 403 caninclude at least one BAW resonator with a patterned mass loading layerin accordance with any suitable principles and advantages disclosedherein.

For example, the front end system 393 can provide a number offunctionalities, including, but not limited to, amplifying signals fortransmission, amplifying received signals, filtering signals, switchingbetween different bands, switching between different power modes,switching between transmission and receiving modes, duplexing ofsignals, multiplexing of signals (for instance, diplexing ortriplexing), or any suitable combination thereof.

In certain implementations, the mobile device 390 supports carrieraggregation, thereby providing flexibility to increase peak data rates.Carrier aggregation can be used for both Frequency Division Duplexing(FDD) and Time Division Duplexing (TDD), and may be used to aggregate aplurality of carriers or channels. Carrier aggregation includescontiguous aggregation, in which contiguous carriers within the sameoperating frequency band are aggregated. Carrier aggregation can also benon-contiguous, and can include carriers separated in frequency within acommon band or in different bands.

The antennas 394 can include antennas used for a wide variety of typesof communications. For example, the antennas 394 can include antennasfor transmitting and/or receiving signals associated with a wide varietyof frequencies and communications standards.

In certain implementations, the antennas 394 support MIMO communicationsand/or switched diversity communications. For example, MIMOcommunications use multiple antennas for communicating multiple datastreams over a single radio frequency channel. MIMO communicationsbenefit from higher signal to noise ratio, improved coding, and/orreduced signal interference due to spatial multiplexing differences ofthe radio environment. Switched diversity refers to communications inwhich a particular antenna is selected for operation at a particulartime. For example, a switch can be used to select a particular antennafrom a group of antennas based on a variety of factors, such as anobserved bit error rate and/or a signal strength indicator.

The mobile device 390 can operate with beamforming in certainimplementations. For example, the front end system 393 can includeamplifiers having controllable gain and phase shifters havingcontrollable phase to provide beam formation and directivity fortransmission and/or reception of signals using the antennas 394. Forexample, in the context of signal transmission, the amplitude and phasesof the transmit signals provided to the antennas 394 are controlled suchthat radiated signals from the antennas 394 combine using constructiveand destructive interference to generate an aggregate transmit signalexhibiting beam-like qualities with more signal strength propagating ina given direction. In the context of signal reception, the amplitude andphases are controlled such that more signal energy is received when thesignal is arriving to the antennas 394 from a particular direction. Incertain implementations, the antennas 394 include one or more arrays ofantenna elements to enhance beamforming.

The baseband system 391 is coupled to the user interface 397 tofacilitate processing of various user input and output (I/O), such asvoice and data. The baseband system 391 provides the transceiver 392with digital representations of transmit signals, which the transceiver392 processes to generate RF signals for transmission. The basebandsystem 391 also processes digital representations of received signalsprovided by the transceiver 392. As shown in FIG. 39, the basebandsystem 391 is coupled to the memory 396 of facilitate operation of themobile device 390.

The memory 396 can be used for a wide variety of purposes, such asstoring data and/or instructions to facilitate the operation of themobile device 390 and/or to provide storage of user information.

The power management system 395 provides a number of power managementfunctions of the mobile device 390. In certain implementations, thepower management system 395 includes a PA supply control circuit thatcontrols the supply voltages of the power amplifiers 401. For example,the power management system 395 can be configured to change the supplyvoltage(s) provided to one or more of the power amplifiers 401 toimprove efficiency, such as power added efficiency (PAE).

As shown in FIG. 39, the power management system 395 receives a batteryvoltage from the battery 398. The battery 398 can be any suitablebattery for use in the mobile device 390, including, for example, alithium-ion battery.

Technology disclosed herein can be implemented in acoustic wave filtersin fifth generation (5G) applications. 5G technology is also referred toherein as 5G New Radio (NR). 5G NR supports and/or plans to support avariety of features, such as communications over millimeter wavespectrum, beamforming capability, high spectral efficiency waveforms,low latency communications, multiple radio numerology, and/ornon-orthogonal multiple access (NOMA). Although such RF functionalitiesoffer flexibility to networks and enhance user data rates, supportingsuch features can pose a number of technical challenges.

The teachings herein are applicable to a wide variety of communicationsystems, including, but not limited to, communication systems usingadvanced cellular technologies, such as LTE-Advanced, LTE-Advanced Pro,and/or 5G NR. An acoustic wave device including any suitable combinationof features disclosed herein be included in a filter arranged to filtera radio frequency signal in a fifth generation (5G) New Radio (NR)operating band within Frequency Range 1 (FR1). A filter arranged tofilter a radio frequency signal in a 5G NR operating band can includeone or more SAW devices disclosed herein. FR1 can be from 410 MHz to7.125 GHz, for example, as specified in a current 5G NR specification.One or more acoustic wave devices in accordance with any suitableprinciples and advantages disclosed herein can be included in a filterarranged to filter a radio frequency signal in a fourth generation (4G)Long Term Evolution (LTE). One or more acoustic wave devices inaccordance with any suitable principles and advantages disclosed hereincan be included in a filter having a passband that includes a 4G LTEoperating band operating band and a 5G NR operating band. Such a filtercan be implemented in a dual connectivity application, such as anE-UTRAN New Radio-Dual Connectivity (ENDC) application.

The acoustic wave filters disclosed herein can suppress secondharmonics. Such features can be advantageous in 5G NR applications.Suppressing second harmonics can provide increased filter linearity.With higher filter linearity, higher peak to average power ratios thatare present in certain 5G NR applications can be accommodated.Suppression of harmonics and/or higher filter linearity can beadvantageous for meeting one or more other specifications in 5Gtechnology.

FIG. 40 is a schematic diagram of one example of a communication network410. The communication network 410 includes a macro cell base station411, a small cell base station 413, and various examples of userequipment (UE), including a first mobile device 412 a, awireless-connected car 412 b, a laptop 412 c, a stationary wirelessdevice 412 d, a wireless-connected train 412 e, a second mobile device412 f, and a third mobile device 412 g. UEs are wireless communicationdevices. One or more of the macro cell base station141, the small cellbase station 413, or UEs illustrated in FIG. 40 can implement one ormore of the acoustic wave filters in accordance with any suitableprinciples and advantages disclosed herein. For example, one or more ofthe UEs shown in FIG. 40 can include one or more acoustic wave filtersthat include any suitable number of BAW resonators with a patterned massloading layer.

Although specific examples of base stations and user equipment areillustrated in FIG. 40, a communication network can include basestations and user equipment of a wide variety of types and/or numbers.For instance, in the example shown, the communication network 410includes the macro cell base station 411 and the small cell base station413. The small cell base station 413 can operate with relatively lowerpower, shorter range, and/or with fewer concurrent users relative to themacro cell base station 411. The small cell base station 413 can also bereferred to as a femtocell, a picocell, or a microcell. Although thecommunication network 410 is illustrated as including two base stations,the communication network 410 can be implemented to include more orfewer base stations and/or base stations of other types.

Although various examples of user equipment are shown, the teachingsherein are applicable to a wide variety of user equipment, including,but not limited to, mobile phones, tablets, laptops, Internet of Things(IoT) devices, wearable electronics, customer premises equipment (CPE),wireless-connected vehicles, wireless relays, and/or a wide variety ofother communication devices. Furthermore, user equipment includes notonly currently available communication devices that operate in acellular network, but also subsequently developed communication devicesthat will be readily implementable with the inventive systems,processes, methods, and devices as described and claimed herein.

The illustrated communication network 410 of FIG. 40 supportscommunications using a variety of cellular technologies, including, forexample, 4G LTE and 5G NR. In certain implementations, the communicationnetwork 410 is further adapted to provide a wireless local area network(WLAN), such as WiFi. Although various examples of communicationtechnologies have been provided, the communication network 410 can beadapted to support a wide variety of communication technologies.

Various communication links of the communication network 410 have beendepicted in FIG. 40. The communication links can be duplexed in a widevariety of ways, including, for example, using frequency-divisionduplexing (FDD) and/or time-division duplexing (TDD). FDD is a type ofradio frequency communications that uses different frequencies fortransmitting and receiving signals. FDD can provide a number ofadvantages, such as high data rates and low latency. In contrast, TDD isa type of radio frequency communications that uses about the samefrequency for transmitting and receiving signals, and in which transmitand receive communications are switched in time. TDD can provide anumber of advantages, such as efficient use of spectrum and variableallocation of throughput between transmit and receive directions.

In certain implementations, user equipment can communicate with a basestation using one or more of 4G LTE, 5G NR, and WiFi technologies. Incertain implementations, enhanced license assisted access (eLAA) is usedto aggregate one or more licensed frequency carriers (for instance,licensed 4G LTE and/or 5G NR frequencies), with one or more unlicensedcarriers (for instance, unlicensed WiFi frequencies).

As shown in FIG. 40, the communication links include not onlycommunication links between UE and base stations, but also UE to UEcommunications and base station to base station communications. Forexample, the communication network 410 can be implemented to supportself-fronthaul and/or self-backhaul (for instance, as between mobiledevice 412 g and mobile device 412 f).

The communication links can operate over a wide variety of frequencies.In certain implementations, communications are supported using 5G NRtechnology over one or more frequency bands that are less than 6Gigahertz (GHz) and/or over one or more frequency bands that are greaterthan 6 GHz. According to certain implementations, the communicationlinks can serve Frequency Range 1 (FR1), Frequency Range 2 (FR2), or acombination thereof. An acoustic wave filter in accordance with anysuitable principles and advantages disclosed herein can filter a radiofrequency signal within FR1. In one embodiment, one or more of themobile devices support a HPUE power class specification.

In certain implementations, a base station and/or user equipmentcommunicates using beamforming. For example, beamforming can be used tofocus signal strength to overcome path losses, such as high lossassociated with communicating over high signal frequencies. In certainembodiments, user equipment, such as one or more mobile phones,communicate using beamforming on millimeter wave frequency bands in therange of 30 GHz to 300 GHz and/or upper centimeter wave frequencies inthe range of 6 GHz to 30 GHz, or more particularly, 24 GHz to 30 GHz.

Different users of the communication network 410 can share availablenetwork resources, such as available frequency spectrum, in a widevariety of ways. In one example, frequency division multiple access(FDMA) is used to divide a frequency band into multiple frequencycarriers. Additionally, one or more carriers are allocated to aparticular user. Examples of FDMA include, but are not limited to,single carrier FDMA (SC-FDMA) and orthogonal FDMA (OFDMA). OFDMA is amulticarrier technology that subdivides the available bandwidth intomultiple mutually orthogonal narrowband subcarriers, which can beseparately assigned to different users.

Other examples of shared access include, but are not limited to, timedivision multiple access (TDMA) in which a user is allocated particulartime slots for using a frequency resource, code division multiple access(CDMA) in which a frequency resource is shared amongst different usersby assigning each user a unique code, space-divisional multiple access(SDMA) in which beamforming is used to provide shared access by spatialdivision, and non-orthogonal multiple access (NOMA) in which the powerdomain is used for multiple access. For example, NOMA can be used toserve multiple users at the same frequency, time, and/or code, but withdifferent power levels.

Enhanced mobile broadband (eMBB) refers to technology for growing systemcapacity of LTE networks. For example, eMBB can refer to communicationswith a peak data rate of at least 10 Gbps and a minimum of 100 Mbps foreach user. Ultra-reliable low latency communications (uRLLC) refers totechnology for communication with very low latency, for instance, lessthan 3 milliseconds. uRLLC can be used for mission-criticalcommunications such as for autonomous driving and/or remote surgeryapplications. Massive machine-type communications (mMTC) refers to lowcost and low data rate communications associated with wirelessconnections to everyday objects, such as those associated with Internetof Things (IoT) applications.

The communication network 410 of FIG. 40 can be used to support a widevariety of advanced communication features, including, but not limitedto, eMBB, uRLLC, and/or mMTC.

Any of the embodiments described above can be implemented in associationwith mobile devices such as cellular handsets. The principles andadvantages of the embodiments can be used for any systems or apparatus,such as any uplink wireless communication device, that could benefitfrom any of the embodiments described herein. The teachings herein areapplicable to a variety of systems. Although this disclosure includesexample embodiments, the teachings described herein can be applied to avariety of structures. Any of the principles and advantages discussedherein can be implemented in association with RF circuits configured toprocess signals having a frequency in a range from about 30 kHz to 300GHz, such as in a frequency range from about 450 MHz to 8.5 GHz.

Aspects of this disclosure can be implemented in various electronicdevices. Examples of the electronic devices can include, but are notlimited to, consumer electronic products, parts of the consumerelectronic products such as packaged radio frequency modules, radiofrequency filter die, uplink wireless communication devices, wirelesscommunication infrastructure, electronic test equipment, etc. Examplesof the electronic devices can include, but are not limited to, a mobilephone such as a smart phone, a wearable computing device such as a smartwatch or an ear piece, a telephone, a television, a computer monitor, acomputer, a modem, a hand-held computer, a laptop computer, a tabletcomputer, a microwave, a refrigerator, a vehicular electronics systemsuch as an automotive electronics system, a robot such as an industrialrobot, an Internet of things device, a stereo system, a digital musicplayer, a radio, a camera such as a digital camera, a portable memorychip, a home appliance such as a washer or a dryer, a peripheral device,a wrist watch, a clock, etc. Further, the electronic devices can includeunfinished products.

Unless the context indicates otherwise, throughout the description andthe claims, the words “comprise,” “comprising,” “include,” “including”and the like are to generally be construed in an inclusive sense, asopposed to an exclusive or exhaustive sense; that is to say, in thesense of “including, but not limited to.” Conditional language usedherein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,”“for example,” “such as” and the like, unless specifically statedotherwise, or otherwise understood within the context as used, isgenerally intended to convey that certain embodiments include, whileother embodiments do not include, certain features, elements and/orstates. The word “coupled”, as generally used herein, refers to two ormore elements that may be either directly connected, or connected by wayof one or more intermediate elements. Likewise, the word “connected”, asgenerally used herein, refers to two or more elements that may be eitherdirectly connected, or connected by way of one or more intermediateelements. Additionally, the words “herein,” “above,” “below,” and wordsof similar import, when used in this application, shall refer to thisapplication as a whole and not to any particular portions of thisapplication. Where the context permits, words in the above DetailedDescription using the singular or plural number may also include theplural or singular number respectively.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the novel filters, wirelesscommunication devices, apparatus, methods, and systems described hereinmay be embodied in a variety of other forms. Furthermore, variousomissions, substitutions and changes in the form of the filters,wireless communication devices, apparatus, methods, and systemsdescribed herein may be made without departing from the spirit of thedisclosure. For example, while blocks are presented in a givenarrangement, alternative embodiments may perform similar functionalitieswith different components and/or circuit topologies, and some blocks maybe deleted, moved, added, subdivided, combined, and/or modified. Each ofthese blocks may be implemented in a variety of different ways. Anysuitable combination of the elements and/or acts of the variousembodiments described above can be combined to provide furtherembodiments. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the disclosure.

What is claimed is:
 1. An acoustic wave filter comprising: a first bulkacoustic wave resonator including a first patterned mass loading layerhaving a first density, the first patterned mass loading layer impactinga resonant frequency of the first bulk acoustic wave resonator; and asecond bulk acoustic wave resonator including a second patterned massloading layer having a second density, the second density beingdifferent than the first density, the second patterned mass loadinglayer impacting a resonant frequency of the second bulk acoustic waveresonator, and the bulk acoustic wave filter being arranged to filter aradio frequency signal.
 2. The acoustic wave filter of claim 1 whereinthe first patterned mass loading layer has a periodic pattern.
 3. Theacoustic wave filter of claim 1 wherein the first patterned mass loadinglayer includes a plurality of strips spaced apart from each other. 4.The acoustic wave filter of claim 1 wherein the first patterned massloading layer includes a metal.
 5. The acoustic wave filter of claim 1wherein the first patterned mass loading layer includes a dielectricmaterial.
 6. The acoustic wave filter of claim 1 wherein the firstpatterned mass loading layer is positioned below a piezoelectric layerof the first bulk acoustic wave resonator.
 7. The acoustic wave filterof claim 1 wherein the first patterned mass loading layer is positionedabove a piezoelectric layer of the first bulk acoustic wave resonator.8. The acoustic wave filter of claim 1 wherein the first patterned massloading layer extends from a first piezoelectric layer of the first bulkacoustic wave resonator a same distance as the second patterned massloading layer extends from a second piezoelectric layer of the secondbulk acoustic wave resonator.
 9. The acoustic wave filter of claim 1further comprising a third bulk acoustic wave resonator that includes athird patterned mass loading layer having a third density, the thirddensity being different than both the first density and the seconddensity.
 10. The acoustic wave filter of claim 1 wherein a resonantfrequency of the first bulk acoustic wave resonator is in a range from0.1% to 10% greater than a resonant frequency of the second bulkacoustic wave resonator.
 11. The acoustic wave filter of claim 1 whereinthe second patterned mass loading layer has a duty factor in a rangefrom 0.05 to 0.95 in a central area of an active region of the firstbulk acoustic wave resonator.
 12. The acoustic wave filter of claim 11wherein the first patterned mass loading layer has a duty factor in arange from 0.05 to 0.95 in a central area of an active region of thesecond bulk acoustic wave resonator.
 13. An acoustic wave diecomprising: a first bulk acoustic wave resonator on the bulk acousticwave die, the first bulk acoustic wave resonator including a firstpatterned mass loading layer having a first density, the first patternedmass loading layer impacting a resonant frequency of the second bulkacoustic wave resonator; and a second bulk acoustic wave resonator onthe bulk acoustic wave die, the second bulk acoustic wave resonatorincluding a second patterned mass loading layer having a second density,the second density being higher than the first density, the secondpatterned mass loading layer impacting a resonant frequency of thesecond bulk acoustic wave resonator.
 14. The acoustic wave die of claim13 wherein the first bulk acoustic wave resonator and the second bulkacoustic wave resonator are included in a same filter.
 15. The acousticwave die of claim 13 wherein the first bulk acoustic wave resonator andthe second bulk acoustic wave resonator are included in differentfilters.
 16. The acoustic wave die of claim 13 wherein the firstpatterned mass loading layer includes a plurality of strips spaced apartfrom each other.
 17. The acoustic wave die of claim 13 furthercomprising a third bulk acoustic wave resonator that includes a thirdpatterned mass loading layer having a third density, the third densitybeing different than both the first density and the second density. 18.The acoustic wave die of claim 13 wherein a resonant frequency of thefirst bulk acoustic wave resonator is in a range from 0.1% to 10%greater than a resonant frequency of the second bulk acoustic waveresonator.
 19. The acoustic wave die of claim 13 wherein the firstpatterned mass loading layer has a duty factor in a range from 0.05 to0.95 in a central area of an active region of the first bulk acousticwave resonator.
 20. A radio frequency module comprising: an acousticwave filter including a first bulk acoustic wave resonator and a secondbulk acoustic wave resonator, the first bulk acoustic wave resonatorincluding a first patterned mass loading layer having a first densityand impacting a resonant frequency of the first bulk acoustic waveresonator, the second bulk acoustic wave resonator including a secondpatterned mass loading layer having a second density, the second densitybeing higher than the first density, and the second patterned massloading layer, the second patterned mass loading layer impacting aresonant frequency of the second bulk acoustic wave resonator; and aradio frequency circuit element coupled to an acoustic wave filter thatincludes at least the first bulk acoustic wave resonator, the acousticwave filter and the radio frequency circuit element being enclosedwithin a common module package.